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How Safe Is Your Food? Investigating the effectiveness of odor-proof bags
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Ryan Jordan
(ryan) - BPL Staff - MLife

Locale: Greater Yellowstone
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 00:09:28 MDT Print View

Companion forum thread to:

How Safe Is Your Food? Investigating the effectiveness of odor-proof bags

Johan Engberg

Locale: Wrong place at the right rime
Bandana on 04/10/2013 00:48:00 MDT Print View

Interestning but not surprising. After having seen trained dogs look for human tracks on pavement, humans in avalanches, munitions, truffle or whatever, it's easy to believe there's no limit.

One important thing to think about when avoiding "scent detection" is wind direction. May be hard to predict bear direction though...

I only have brief experience with hiding food in bags in the smokies one night a couple of years ago. Since where I usually roam there's no need for food-bags it was all new to me. Turned out ok but my measures where literally worthless if a bear would have been close.

But to the question! What's the brand and the weight of the see-through bandana the officer in the 4th picture has over his eyes?
I see multi-purpose use, sunglasses and cap. :)

Travis Leanna
(T.L.) - MLife

Locale: Wisconsin
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 00:58:44 MDT Print View

Well done. I'm glad this experiment was completed, and from a layman, it is a little surprising. Thanks.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 01:06:15 MDT Print View

Way to go!

Demonstrating marketing 1, science 0, for the claims.
Most excellent study.


Philip Marshall
(philthy) - MLife
Can never ignore an article with dogs in it... on 04/10/2013 01:09:32 MDT Print View

Wow, this is really great, well done organising this.

I find the results unsurprising and a good reminder that there aren't any shortcuts to bear safety.

Travis Leanna
(T.L.) - MLife

Locale: Wisconsin
the animal kingdom on 04/10/2013 01:13:12 MDT Print View

The Animal Kingdom never ceases to amaze. I'd MUCH rather hear about this kind of thing in the news than the nonstop stupidity of our fellow humans.

Bradley Danyluk
(dasbin) - MLife
Quantum noses on 04/10/2013 02:05:02 MDT Print View

Amazing stuff. Many thanks for such a thoughtful and meticulous study.

(jpovs) - F

Locale: Arrowhead
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 05:29:34 MDT Print View


Edited by jpovs on 06/27/2014 22:21:26 MDT.

Tony Ronco
(tr-browsing) - MLife
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 06:15:30 MDT Print View

Excellent Study - Much Thanks for publishing it.

Raises a lot of interesting questions in my mind ... here are two:

I wonder about the rates of permeability ... given how quickly the dogs found their targets it doesn't seem like doubling the bags would help.

I also wonder about vacuum sealer bags used for home dehydrated meals. (If odiferous smells can get permeate out, then can O2 permeate & get in? ... same question about commercial freeze-dried offerings)

Ok, Art - when are you going to publish the next set of experiments? :-)

Mike V
(deadbox) - F - M

Locale: Midwest
RE: "How Safe Is Your Food? Investigating the effectiveness of odor-proof bags" on 04/10/2013 06:34:54 MDT Print View

excellent article! I am not surprised by the findings, although I still believe OP sacks likely reduce odor transmission better than a standard zip lock and still have some value when used in conjunction with a proper hang or inside of a bear canister.

Ben Crocker
(alexdrewreed) - M

Locale: Kentucky
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 06:50:51 MDT Print View

Great work. I have always been sceptical of the OP bags and have not purchased them. I assumed they were no better than ziplocks. But I am a little surprised though that neither seems to have much useful effect.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 08:08:41 MDT Print View

Thanks for the nice comments, guys. We had fun performing this study and the dogs thought it was a great game.

"I am a little surprised though that neither seems to have much useful effect."
@Ben- We only looked at whether the odor-proof bags performed better than ziplocs. We did not address the question of whether either had a useful effect at all. Here is an abstract suggesting that ziplocs may decrease bears ability to smell food, though one has to wonder whether the difference between 6 and 9 seconds is significant in a practical sense.

Wilderness & Environmental Medicine
Volume 21, Issue 4 , Pages 375-376, December 2010

Ziploc Bags for Preventing Bears from Smelling Food

Background.—Wilderness activities occasionally result in
bear-encounters. To deter bears from detecting food scents, the
American Bear Association recommends double-bagging food
carried into the wilderness.
Objective.—Our objective was to determine if food sealed
in double-bagged Ziploc bags would decrease the ability of
bears to detect food scents as compared to food in unsealed
Ziploc bags.
Methods.—This was a prospective randomized singleblinded
study performed on bears at Northwest Trek Wildlife
Park, WA. Two black bears (Ursus americanus) and 2 brown
bears (Ursus arctos) were presented with open buckets in front
of their enclosures: one concealing food wrapped in 2 layers of
Ziploc bags and another with empty Ziploc bags. The time the
bears spent at each bucket was recorded for 30 seconds. In the
first phase, Ziplocs were open; in the second, Ziplocs were
Results.—The average time the bears spent at the open
Ziplocs with food and open Ziplocs without during the first
phase of the experiment was 9.573 and 6.613 seconds, respectively
(N _ 75). The average time spent at the closed Ziplocs
with food and closed Ziplocs without in the second phase of the
experiment was 6.25 and 6.8875 seconds, respectively (N _
80). The standard deviation for all average times was 1.5
seconds. An independent samples 2-tailed t-Test demonstrated
a statistically significant difference (P _ 0.032) when compar-ing
the time the bears spent at the open Ziplocs with food to the
closed Ziplocs with food. There was no statistically significant
difference between the controls from both phases of the experiment
(P _ 0.854).
Conclusions.—The bears spent a statistically significant
greater time at the open Ziplocs with food compared to the
closed Ziplocs with food. These data suggest that sealing food
in 2 layers of Ziploc bag may decrease the ability of bears to
detect the scent of food from within. We advise following the
ABA recommendations.

Clark M. Rosenberry, MD
David C. Hile, MD
Troy H. Patience, BS
Fort Lewis, WA, USA

Richard L. Sartor, MS
Angela K. Gibson, MS
Northwest Trek Wildlife Park, WA, USA

@Tony- I can answer your question about foodsaver bags, though not with a direct comparison. I had relied on the police officers to provide the "scent packets" for the study. Naively, I only questioned type and weight of the product, but not how they were packaged. After the study, I theorized that the seal must be the weak link in these bags and proposed a second study where we would investigate bags that were heat sealed to remove the opening. The officers laughed and told me the dogs would find them anyway. As it turned out, the drugs we used were sealed in foodsaver bags and then wrapped in a heavy canvas outer covering to protect the dogs from accidental exposure. I don't pretend to understand the intricacies of olfaction, but I developed a tremendous amount of respect for the dogs over the course of this study. Scent will find a way.

Bob Bankhead
(wandering_bob) - MLife

Locale: Oregon, USA
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 08:10:53 MDT Print View

I'll be curious to see what the manufacturer of OP Sacks has to say - if anything.

Is it safe to assume you provided them with a courtesy copy of your article?

Thanks for your time. Please keep us advised.

Phillip Asby

Locale: North Carolina
Interesting on 04/10/2013 08:22:36 MDT Print View

I'll say it's things like this (and many others) that make BPL such a useful resource for a newbie like me - and by the responses for experienced backpackers as well!

This weekends trip with my sons Scout Troop is to Panthertown Valley, NC which is located within a NC designated black bear sanctuary and was subjec to a National Forest Service bear alert regarding some bears entering campgrounds and taking down bear bags.

I've been spending some time looking at bear safety myself, and our Troop has done a session on bear safety with the scouts. I have a bear canister I'll probably take along since I have it (UDAP No Fed Bear I got at STP for a good price with coupon) despite the weight. I'd been thinking about the odor sacks for my stuff as well given that the canister does nothing for odors and this article gives me pause to consider whether it is worth the effort.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: Interesting on 04/10/2013 08:30:16 MDT Print View


It is obvious that you will need a "Bag Handler" who has NO food/scent odors.

No foods in the pack.
Sitting 100 yards away during food prep and trailside lunches.
If this individual eats, s/he will have to be naked, and then take a bath.
I'm sure there are other considerations as well.

Best of Luck.

Edited by greg23 on 04/10/2013 08:32:06 MDT.

Craig W.
(xnomanx) - F - M
Interesting on 04/10/2013 09:07:42 MDT Print View

Thanks for confirming this. I've already had many very experienced thru-hikers tell me OPSAKs are useless...good to know it's not just speculation.


I suspect you could've made a lot more money by forwarding this article to High Times Magazine instead of BPL. This info could potentially keep a lot of "entrepreneurs" out of trouble.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
re: Entrepreneurs on 04/10/2013 09:11:17 MDT Print View

I asked the officers what would happen if the dogs couldn't find the bags. They told me that they would all buy stock in the company before the article got released.

Luke Schmidt
(Cameron) - MLife

Locale: The WOODS
Vacuum Sealed Bags? on 04/10/2013 09:14:37 MDT Print View

Did any of the officers mention people using vacuum sealed bags to fool dogs?

For lack of a better option I'm thinking I might vacuum seal individual meals and wash the outside of those meals very thoroughly. Obviously there will still be odor I'm just hoping it will be less odor then if I'd left a hunk of greasy summer sausage out.

For black bear I'm not too worried. Where I hike they are hunted and unlikely to bother me. Grizzly country would be the one place I'd go overboard with the whole vacuum sealing idea.

Stephen Barber
(grampa) - MLife

Locale: SoCal
Great job! on 04/10/2013 09:22:56 MDT Print View

Excellent work, Ari! I'm glad this research got published - it's just the kind of work that we need here on BPL!

I have a great deal of respect for dogs' scenting abilities, and seriously doubt that bears are any less able. Depending on "scent proof" bags is obviously not a viable technique for food safety in bear country.

Thanks again, and be sure to give your officers and dogs a big "Thank you!" from BPL!

John S.
(jshann) - F
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 09:25:47 MDT Print View

Kyle Meyer

Locale: Portland, OR
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 09:51:42 MDT Print View

One thing missing from this study is proximity. I certainly understand dogs (or any creature) identifying food when it's literally inches from it's nose, but I'm curious what the rate of detection would have been from 3 or even 6 feet away, emulating the distance a bear bag would be from the snout of a bear. Additionally, trapping odor in a locker with the ability to extract the air easily via a vent would seem to enhance the ability for a dog to detect the bags.

In open air, at 6 feet away, my guess is the results would be very different.

That said, thank you so much for doing this study. We need more of this on BPL.

Daniel Pittman
(pitsy) - M

Locale: Central Texas
Somewhere... on 04/10/2013 10:01:52 MDT Print View

Out there waiting for you, is a bear. He can smell what you're thinking. He can smell what the weather is going to do. He can smell your car's tire pressure. He can smell that your bike isn't shifting right. He can smell how Stonehenge was built. He can smell the origin of the Universe. He can smell everything.

Courtenay Ennis
(courtenayennis) - MLife

Locale: Southwestern BC
Opsak seal sucks on 04/10/2013 10:10:02 MDT Print View

It's great to know there is little practical difference in odourproofness between Opsak and Ziplok.

One observation from using both:

Odour permeability aside, the actual seals on Opsak bags are, in my experience, terrible. The bags can open in packs far more readily than Ziploc seals. Even if the odourproofness was perfect, it's a huge problem that the seals are so weak. I was putting everything in my Opsaks in Ziplocs, first, as a backup, but now I'll just forego the Opsaks altogether.

If Opsak could greatly improve their seal, I might still buy them, in spite of this study, for the additional piece of mind, but in lieu of this study, with their current seals... no point whatsoever.

Thanks for the great study! Love the care taken in designing it.

John Coyle

Locale: NorCal
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 10:28:12 MDT Print View

This article has saved me money, because I don't see any reason to buy OP sacks again. Hard as it is to take for light and ultralight backpackers, it appears the the only sure way to prevent food from being destroyed by bears or other animals is to use a hard sided bear canister. Hats off to BPL for publishing this article, because you are going to get some flak from OP sack companies, I can guarantee you that.

Rob E

Locale: Canada
distance+wind on 04/10/2013 10:32:34 MDT Print View

If a bear is a few feet from food in an odour proof bag I have no doubt that it will zero in pretty quickly.

To me the value of the odour proof bags are when the bear is a few hundred meters away, or some wind. The odour proof bags might possibly mute the smell enough to make it uninteresting in comparison to other natural (or unnatural sources), or possibly increase the difficulty in vectoring in on the source. If nothing else my opsak is coming along anyway to mask the smell of esbit, a task it does admirably.

I look forward to scorning odour proof bags becoming BPL dogma. I will add opsaks to my growing list of things I do or use but don't mention here any more, including but not limited to: trekking poles, hydration bladders, light hikers, white gas stoves, fleece, knife instead of scissors, bear spray, venturing out in the rain, drinking gatorade and using toilet paper.

(Edit: full disclosure, as a forum member, I did not read the article)

Edited by eatSleepFish on 04/10/2013 10:44:38 MDT.

Hk Newman
(hknewman) - MLife

Locale: Western US
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 10:33:50 MDT Print View

Interesting, though the cover photo is reminiscent of American high school locker sweeps since the late 1970's (kind of had a surprise opening up BPL this AM). By the time I slather blueberry preserves and peanut on a bagel for Lunch #1, I figure these smells coat the outer part of any baggie regardless. Still a very good study but wonder what the lifespan of a ziploc vs. odor-proof bag is if washed after every trip. Got my odor-proofs with my Ursack, occasionally wash and reuse it, whereas with ziplocs they are tossed (unless green-minded girlfriend insists on washing and reusing them.. yeah, she wasn't even a hippy chick either). Think most toss Ziplocs, so further study is likely pointless.

Herbert Sitz

Locale: Pacific NW
Re: distance+wind on 04/10/2013 10:46:15 MDT Print View

I tend to agree with Rob E. I no longer have premium membership to read the BPL article, but it seems to me there is a big difference between testing at close range and at more of a distance.

I know I can reliably and quickly distinguish between a faint odor and absence of odor at very close range. As distance increases that ability disappears. I see no reason why this would be different with dogs or bears. And I'm pretty sure that as distance is added the ability to discern odor from an OPSAK would fail more quickly than ability to discern odor from a ziploc.

I csn personally confirm that there is a big difference between the amount of odor that escapes a regular ziploc and what escapes an OPSAK. I can't smell odor from OPSAK even at close range, although of course I'm not surprised that a dog or bear could. But increase distance of dog or bear from ziploc and OPSAK to 10 yards, 100 yards, a quarter mile, or longer, and I suspect at some distance the animal will be able to smell contents of the ziploc but not be able to smell contents of OPSAK. Of course that's much harder to reliably and easily test.

I say all of this with belief that bears have powers of smell greater than any dog. I believe there are studies that show that, although for now I'm satisfied with this from Wikipedia: ". . . the Silvertip Grizzly found in parts of North America, ha[s] a sense of smell seven times stronger than that of the bloodhound. . .". Wikipedia entry on Olfaction

Edited by hes on 04/10/2013 10:53:47 MDT.

Will Tatman
Opsaks on 04/10/2013 11:02:37 MDT Print View

Well done article, I appreciate the thoroughness.

As someone who uses OpSaks exclusively for food protection, I will now have to do some further thinking about food selection and packaging. As a vegan, I don't interact much with Cheese or Salami, which I assume might hold the titles for 'stinkiest trail foods' But I do hike with Peanut Butter, a top contender. I tend to just throw a jar straight into an Opsak along with my day-to-day meals (themselves in a gallon bag per day), and one extra ziplock full of trash. At the end of the day, I seal up the opsak, wrap it in a wind jacket, and use it as a pillow. Same method I used on the GET last year with no issues. So, not terribly comforting to read this article, but until I know more about how proximity, layering, and food selection factor in, not enough to deter me from continuing to use OpSaks instead of hanging or canisters (at least in the desert/mountain SW).

John Nausieda
(Meander) - MLife

Locale: PNW
Re: Opsak seal sucks on 04/10/2013 11:02:39 MDT Print View

There are ways to beef up the sealing of an Opsak by using this product at Amazon.

Also wondering if Nylofume bags were mentioned or could be studied in the future.

Stephen Barber
(grampa) - MLife

Locale: SoCal
"odor-proof" bags vs ziplocks on 04/10/2013 11:04:46 MDT Print View

@ Rob and Herbert:

Since you didn't read the article, let me summarize it: There was no real or statistical difference in the dog's ability to locate drugs enclosed in either a ziplock or OP bag.

If there is no difference at close range, enclosed in a locker, indicating that about the same quantity of scented molecules are escaping each type of bag, I don't see how you can expect a difference at a distance when the food is enclosed within a bear bag or pack?

Billy Ray
(rosyfinch) - M

Locale: the mountains
odor proof bags may still do some good on 04/10/2013 11:07:02 MDT Print View

If an 'odor-proof' bag just slows down the emissions of smells, then it may do you some good. Reduced emissions my reduce the distance at which bears can pick up a trace of things inside. In other words, a bear may need to be, say, closer than 100 yards to pick up the smell of something in any plastic bag. Whereas a bear a half a mile away may pick up the scent of food outside of a bag. So it could make a difference as to whether a bear comes to your camp or not.

In addition, it seems to me the above study did not determine if the Op Sack could reduce odor emissions to a lower level than that of a regular zip lock. It may be that it does, but both were over the threshold of what was required for the dogs to pick up the scent in such a small area as was used.

That's my 2 cents.

Using the above logic it may be a good idea to line your bear canister with a plastic bag.


Andrew Zajac

Locale: South West
great study on 04/10/2013 11:07:14 MDT Print View

I think this study was great and shows that the most important aspect of avoiding negative interactions with wildlife is your behavior. I also really appreciated the inclusion of some statistics. Speaking from the perspective of finishing a masters thesis in ecology, statistics can get nit picky to a ridiculous level. This is usually (from my perspective) to no appreciable gain in understanding or interpretation of the data, so I won't nitpick methods. However, there are accepted ways of reporting these statistics that allow the reader to know what tests were performed and what the results are. These can be found with a quick google search and their inclusion would be much appreciated.

David Wood
(RedYeti) - MLife

Locale: South Eastern UK
OP Sacks help but they are not really OP on 04/10/2013 11:08:12 MDT Print View

I've carried a small ziplock bag of curry spices for livening up meals in the past - trouble is everything in the pack smells of curry by the end of a weekend (it should be obvious I'm not talking about bear country here).

However, placing the spices in an small OP sack completely removed the problem.

Interestingly though - I could just smell the spices through the OP sack if I sniffed at it up close.

I've also used them when carrying out empty cans of fish we'd eaten on really long hikes (multi-week) where we could resupply at huts regularly but only dump rubbish occasionally and hadn't good access to detergent based cleaning. The smell of three day old cans of fish cannot be disguised easily in a pack. The OP sacks solved that.

Just pointing out that (as Ari mentioned above) it's not that they have no effect at all, just that it's not 100% as they claim. There are uses for them, and maybe they even reduce the chances of a bear catching the scent - but that's likely to remain conjecture.

Heather Branch
thanks for the study! on 04/10/2013 11:17:29 MDT Print View

I debated whether to renew my BPL membership. This article alone makes me glad I did! I will continue to use my Backpacker's Cache bear barrel [with liner bags and twist locks], despite its weight. I am glad to see I am not the only one who found the OPSak closures terrible. It would be smart if they improved the closures. What I do is put essential food in my bear barrel, put the barrel well away from my site at night, and start out with overflow I could survive without [e.g. coffee and my extra night freeze dried food package] in an OPSack hung in a very light cloth bag at bear bag height etc dimensions or as close as possible. Coffee is pretty essential for many of us, I know, but I always put caffeine pills in the barrel as backup:)

Mary D
(hikinggranny) - MLife
My own experiment with OP sacks and dog on 04/10/2013 11:23:19 MDT Print View

I did a similar experiment a few years ago, using dry dog food with zippered freezer bags (Ziploc brand) and with OP sacks (Loksak brand), and my Labrador/Golden Retriever cross dog (service dog reject). I was concerned because after I packed my dog's kibble into single-serving freezer bags, I could smell the food through the bag, and my nose isn't very sensitive. My results contradict this study.

I tried two layers of freezer bag. That worked for me, but when I left it on the floor, my dog immediately pounced on it and tried to chew into the bags.

I then put a single freezer bag with dog food inside an OP Sack and left it on the floor. My dog walked right by it several times without noticing the smell.

I ran this trial several times, with pretty much the same results. The only difference was that my dog became conditioned to associate a plastic bag on the floor with food, so after a couple of replications he started sniffing the OP sack before moving on. He still did not detect the food inside.

Admittedly, my dog, although of a hunting breed, has never been specifically trained to follow scents, but his food, for him, was an extremely powerful motivator. To motivate him more, I ran the tests just before dinnertime (which caused a lot of barking). Since he didn't smell his food inside the OP Sacks, I had to assume that the OP sacks are at least somewhat effective. The single freezer bag plus OP sack was definitely far more effective than doubled freezer bags.

It may be that those "controlled substances" have a more powerful smell than dry dog food. Or it may be that my dog has a lousy sense of smell. But at least with the OP sacks, I didn't have to worry about my dog getting into his or my food!

Since bears reportedly have a much stronger sense of smell than do dogs, both this study and my one dog study may be moot. However, I have read several anecdotal reports from reliable persons of a bear walking right by a hanging OP sack without investigating it (in most cases the OP sack was inside an Ursack). Maybe the bear wasn't hungry? Or had a head cold?

I will continue to use odor-proof sacks, although I would never rely on them alone, only as a supplement to my Ursack or canister. Nor would I use them to store food inside my tent. But I have demonstrated to my own satisfaction that OP sacks keep my dog out of the food!

PS: I fully agree with others above about the OP sack seals; they're horrible! I plan to try the Nylafume bags, although my dog won't be with me this summer.

I'd love to see the results of a similar trial using mice or other rodents. I had one get in my car one time while I was on a 3-day backpack trip; it ate most of an apple I left on the front seat. It also evidently investigated an OP sack in the back of the car that contained food for a subsequent trip. There were mouse droppings nearby, but no evidence the sack had been chewed. I never figured out how the mouse got in my car, but another backpacker reported the same thing happening at the same trailhead a week before.

Edited by hikinggranny on 04/10/2013 12:14:26 MDT.

Herbert Sitz

Locale: Pacific NW
Re: "odor-proof" bags vs ziplocks on 04/10/2013 11:37:19 MDT Print View

Stephen -- The test is what I assumed it was. That test does not indicate that the "same quantity of scented molecules are escaping each type of bag". It indicates, or is at least consistent with, there being enough molecules escaping each type of bag for both to be easily detectable by the animal, even for them to seem roughly equally strong at small distances. As distance increases, however, if one bag is allowing fewer molecules to escape then it could become undetectable sooner than the other.

I'm not saying I know this is the correct explanation for the test's results. I'm saying that the above explanation is consistent with (1) common sense, (2) my own experience that OPSAKs let out less odor than ziplocs, and (3) the BPL test.

To claim that there is no difference between OPSAKS and ziplocs is inconsistent with my own experience (there's a clear difference for me and other people), so it's hard for me to believe that there is "no difference" between them for dogs and bears. I'm not saying the test was wrong; I'm just suggesting that the conclusions people are drawing from it are stronger than the results of the test warrant. That is, there is another explanation for why there seems to be no statistical difference b/w OPSAKs and ziplocs for dogs at close range, and that explanation squares better with my own experience (and with common sense that as you make a barrier stronger (e.g, double bag vs. single bag ziplocs), fewer items will cross it).

Edited by hes on 04/10/2013 11:42:28 MDT.

Rob E

Locale: Canada
Re: "odor-proof" bags vs ziplocks on 04/10/2013 12:22:20 MDT Print View

Stephen, the difference between the ziplocks and the odour proof bag has to do with absolute detection levels and dilution. Close enough the scent density coming from both bags is higher than the absolute detection level of the dog, but further away when you have dilution and spreading, it might become significant enough to drop below the absolute detection level.

I will use a rough analogy, so bear with me (pun intended): If I can hear both a whisper and an airhorn from 1 foot away, should I expect to be able to hear both 500 feet away? Up close sound volumes from both sources are above the absolute detection level of my ears, but further away the drop in energy manifests itself as an inability to hear the whisper.

Edited by eatSleepFish on 04/10/2013 13:00:14 MDT.

Willie Evenstop
(redmonk) - F

Locale: Greater Yellowstone Ecosystem
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 12:29:58 MDT Print View

Once the dogs knew there was something to find, they worked hard for their reward.

At first the dogs were playful, but once conditioned to realize they were in the room until they found the drugs....

Dogs are highly conditioned to please their worker.

How many false positives were there in a locker room with no drugs given the same conditioned dogs ?

Edited by redmonk on 04/10/2013 12:32:33 MDT.

Bruce Warren
(Aimee) - F - MLife

Locale: South Texas
Raccoon test for Investigating the effectiveness of odor-proof bags on 04/10/2013 12:36:34 MDT Print View

I expected that result. I bought a pack of those bags 6 years ago. After working at Dow Chemical for a while, I was under the opinion that no thin plastic polymer will block the passage of aromatic hydrocarbons for long. Only metal does. I did a raccoon test on my porch using the aluminum coated anti-static bags sold for storing circuit boards. See them at, they are much cheaper and come in lots of sizes. They also totally block moisture and do a good job on blocking oxygen. I have stored crackers in an antistatic bag for two years and they were not stale.

I carefully put cat food inside the anti-static bag and made sure nothing touched the outside. I zipped it up good and laid the bag on the porch. Oscar the Raccoon had been eating the cat food from the bowl for a few weeks. With no food in the bowl that night, I checked the next morning. I saw muddy paw prints on the anti-static bag, but he did not chew on it at all. That told me that no bear will smell it either. But one caveat, after using an aluminum coated bag a few times the aluminum coating will get scrapes or maybe tiny holes. I wrinkled a bag all over for a few minutes and dragged it over my gravel driveway a few feet. Repeating the same Oscar test, he ripped open the bag and ate all the food. There were no holes when I did a water test. So put your anti-static bag inside another bigger one when you use it; making two layers, treat it gently and it will last a long time with no odor leaks

Jay Wilkerson
(Creachen) - MLife

Locale: East Bay
How safe is your food? Investigating the effectiveness of odor-proof bags. on 04/10/2013 12:40:12 MDT Print View

Excellent read and very informative! Wonder if freezer bags make a difference?

Mitchell Rossman

Locale: Minneapolis-St. Paul
Re: Food Bags on 04/10/2013 12:47:11 MDT Print View

Very good study!

As a Ph.D. Chemist, I find this problem to be very interesting.

However, if you did develop a truly odor-proof bag, you might get a visit from your local DEA agent.

Walter Carrington
(Snowleopard) - M

Locale: Mass.
Odor proof bags: nylofume, hunter's scent proof bags vs contractor bags. on 04/10/2013 12:50:52 MDT Print View

Many thanks for doing this careful study.

I have asthma and am very sensitive to some chemicals used for cleaning. I've put my clothes in nylofume, hunter's scent proof bags and black plastic garbage and contractor bags to prevent my clothes from picking up these odors when traveling. The nylofume and hunter's scent proof bags are much better than other plastic bags at keeping out chemical odors -- the odor detector was my [human] nose. So odor proof bags reduce the odors passing through. On the other hand, it is impossible for a hiker to be as careful as the experimenters to avoid contaminating the outside of the bag.

But I doubt that this makes much difference for food bags versus bears. I think most of our guesses on how well various tactics work is based on our experience of human abilities. Dogs or bears have abilities that are difficult for humans to really comprehend.

Edited by Snowleopard on 04/10/2013 12:52:37 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 13:15:33 MDT Print View

Many years ago, before we had bear canisters in Yosemite, we had to hang our backpacker food at night. Still, the black bears knew where to look, and they climbed the trees to pursue the Mountain House prey. We were looking for a way to mask the food odor, so we started using moth balls. We would place a moth ball in the top of each food bag that was hung in the tree. For a while, it looked like that was going to work. Then some black bear stumbled onto the food anyway, and it got a good whiff of the moth balls. So then it associated food smell with the smell of moth balls, so the moth balls became more of an odor attractant than a mask. The entire experiment was a failure.


Kirk Nichols
(kirknichols) - MLife

Locale: Intermountain West, Alaska
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 13:47:08 MDT Print View

Reynolds Oven baking bags are Mylar. I have human nose tested them and no one (human friends) could detect the freshly ground coffee inside though they could smell the grounds through six layers of zip-lock bags. Are the dogs available for another round of testing?Food bags inside an electric bear fence The food bags in the image are inside an electric bear fence that runs on one "D" cell.

Edited by kirknichols on 04/10/2013 13:49:31 MDT.

Stephen Barber
(grampa) - MLife

Locale: SoCal
non-odor proof bags on 04/10/2013 13:48:59 MDT Print View

Rob and Herbert: You're right, I'm wrong on specific molecules dispersion rates. The test doesn't measure absolute rates.

However, the fact that both bags remain detectable by a critter that has only 1/7th the sensitivity of a bear (according to some reports) strongly suggests to me that the difference in real life is minimal. Smells do seem to penetrate the ziplock more quickly than the OpSak, but both are penetrated and dispersed.

This is the first time I've seen OpSak vs ziplock bags actually tested in a controlled situation. Anecdotes are interesting and suggestive for more(controlled) experiments. This test bears (again the pun!) more weight to me than a ton of anecdotes, to the end that, given the permeability of the OpSak bag, its poor seal and its expense, I will not be buying or using anymore until further testing shows the OpSak or its improved offspring to actually block odors. The OpSak's minimal usefulness in blocking odors is not something I care to rely on.

Neither I nor my dogs have ever noticed any difference between ziplocks and OpSaks re smells.


The anecdote regarding metal covered plastic bags is interesting - there's a good line to follow up with testing and development.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
General comments, scent theory, and some specific answers on 04/10/2013 13:57:50 MDT Print View

Lots of great discussion points!

Some general comments: Remember that this study is an experimental model. It is left up to the individual reader to determine how applicable he or she feels the results are to their intended use of the product. Using this model, we were not able to demonstrate any differences between the odor-proof bags and ziplocs. This doesn't mean that there aren't any. As discussed in the article, the dogs work at close range and are trained to signal on even minute amounts of the substances in question.

On the other hand, I have yet to see any strong scientific evidence to suggest that the bags do work any better than ziplocs. Without that proof, and with reasonable evidence to the contrary, why should I blindly believe the theory?

In the end, I believe that our conclusion was appropriate and not overstated. The bags are not 100% odor-proof as advertised. Not only did the dogs find them, but even long after the bags had been removed, dogs would repeatedly signal on the open lockers that had previously held study bags. Scent had been transmitted to the immediate environment.

Specific responses:
@Kyle- thank you for the kind words. I agree that proximity is a limitation of the study. However, the dogs' range is much longer than you think. The handlers like to talk about scent cones. Picture a 3 dimensional structure, heaviest at the source, and radiating outward in a cone-like pattern. The dogs are not actually searching for the object locker by locker as we would do, but instead run laps until they intersect the scent cone. It is very obvious when this happens as their behavior suddenly changes and they practically fall over themselves in their hurry to reverse direction and follow the cone. Study bags contained as little as 5 grams of scent, and as described earlier, this was vacuum sealed in freezer (foodsaver) bags, then wrapped in heavy canvas, then sealed in the study bag. So we are already talking about a trace quantity of scent that is doubly wrapped. Despite this, we saw the dogs hit scent cones from 10-15 feet away. Then they'd run straight to the appropriate locker. How big would the scent cone be when we are talking about 3-5 pounds of food, a stinky odor source approximately 320x larger than what we used and carried by the wind? I'm guessing it would be a pretty large cone.

@Luke and Jay- see my first post in this thread and the details above. Vacuum sealed freezer bags did not prevent odor transmission.

@John- we did not assess the nylafume bags, but may yet do so in an upcoming larger scale study. However, after this pilot study, my enthusiasm for doing so is low. I went into this first study not knowing what we would find (to the officers' credit, they never doubted the dogs for a second). Now that I've seen the dogs at work, I have little hope that a pack liner with a giant hole in the top would have any chance. We are hoping to look at some heat sealable mylar bags, but I will include a couple other odor-proof options if we can do so without making the project too cumbersome for the dogs and handlers.

@Rob, Bill, Stephen, and Herbert- Interesting discussion. We used the timed trials in our model to hopefully pick up on subtle differences between ziplocks and odor-proof bags, and were unable to detect a difference. To definitively answer your question, I think a large scale in situ study is probably needed.

@Redmonk- No false positives. When they knew, they knew, and they would bark and hit the lockers until acknowledged.

@Kirk- heat sealed mylar will be evaluated hopefully next month.

I appreciate all the comments and feedback even if, in the interest of space, I have not responded personally. Thanks again.

(jpovs) - F

Locale: Arrowhead
Re: General comments, scent theory, and some specific answers on 04/10/2013 14:45:36 MDT Print View


Edited by jpovs on 06/15/2014 14:29:17 MDT.

Richard Colfack
(richfax) - MLife

OPSAK on 04/10/2013 15:01:22 MDT Print View

Excellent article. No longer will I waste good money on OPSAKs. I've always been unimpressed with their durability and despise the crappy closure (not too mention their ridiculously high cost for a Ziploc bag) but I always put up with this thinking it helped keep bears from slaughtering me in the tent.

Roleigh Martin
(marti124) - MLife

Locale: Moderator-JohnMuirTrail Yahoo Group
Bruce, thanks for the posting about anti-static bags on 04/10/2013 15:06:15 MDT Print View

Bruce, thanks for the posting about anti-static bags.

I looked at web site for choices. The anti-static bag choices are here:

Postscript: I see there are two types of anti-static bags, those that are poly-based and those that are aluminum based. Uline has the aluminum based ones here:

I wonder how these anti-static bags compare with biohazard specimen bags.

The Nyloflume bags look interesting but I see (a) that you should always use two of them, per recommendation, and secondly, they do not have a ziplock. A good ordering place is here though:

In all 3 alternative bag choices. It would be nice to know which of the 4 (the 4th being OP bags) work best. 4 and 5 if you distinguish between the two types of anti-static bags.

Edited by marti124 on 04/10/2013 15:18:28 MDT.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 15:25:49 MDT Print View

Dr. Jutkowitz, just to close any potential avenues of debate, I would have expected a set of empty bags be included in the same search tests, to eliminate the possibility that the dogs were keying on the plastic smell, latex smell, perhaps the powder on the latex of the bags themselves or something else the experimenters were doing to the bags unintentionally...a mere quibble.

Regardless of the dispersive effect of gases, I think it is safe to say that reliance on OP sacks as the first line of defense against bears is probably not a good thing. Even if a perfect seal, with no scents of edibles on the outside of the bag, could be managed at home or during packing, it would be impossible to maintain in the field. Coupled with the far better sense of smell, usually rated between 2 and 20 times better than a dogs, depending on who you are listening to, and, the rather lengthy time in which foods are normally hung, about 7 hours or about the average sleeping time for a person and usually at night when vision is usually not the primary sense, I do not believe dispersion to be much of a consideration. If the OP sack leaks, it likely leaks enough to be smelled by proximal bears, black or brown. If the dispersive area drops from (an example only) from say 50' to 25' it would reduce the area in which a bear would detect it by about 2/3, but NOT prevent him from breaking into and eating your food. This is more absolute or boolean, he has it or he doesn't. Hey, ha, I prefer NOT to play statistical games with my stomach..."I have food or I don't" doesn't really make sense, only "I have food." I completely agree with your conclusion.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
Re: latex on 04/10/2013 15:38:17 MDT Print View

James- I agree that a no-drug control would have been a great addition. As far as the dogs cuing in on latex scent, this is a vet school student locker room. Lockers and lockers full of latex gloves, plastic bags, dog smells, medicinal smells, etc

Edited by Ike on 04/10/2013 16:02:34 MDT.

Randall Raziano
(rrazian) - MLife

Locale: SW Colorado
Excellent Review. on 04/10/2013 15:54:06 MDT Print View

I was surprised by the result, and this will directly impact the steps I take to avoid bear encounters. Thank you!

rogerio brito
(kafer4life) - MLife

Locale: North Country
Man you guys Rock!! on 04/10/2013 16:05:41 MDT Print View

Wow, I seem to have fallen to the victim of good marketing. Good thing I am cheap and bought them at a discount away from big box stores and with a discount. Well at least they will keep everything dry until I finally get around to making my Cuben food bag. Thanks guys a great read either way. Since I already own them I might as well continue to use them for the slightest bit of extra help they may give.

Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 16:24:10 MDT Print View

Great article!

Another thought about bears -- hike were they ain't. In other words avoid popular areas where bears know how to find an easy meal.

Bruce Warren
(Aimee) - F - MLife

Locale: South Texas
Re: Bruce, thanks for the posting about anti-static bags on 04/10/2013 16:45:43 MDT Print View


I just remembered I also had Oscar test military MREs. They are packaged in thick aluminum foil/plastic bags. Oscar the Raccoon just walked all over them... oblivious to the delicacies inside. You can burn up the empty MRE bags with a little bit of aluminum foil remaining that you can carry out. If you carry only MREs no animals will bother your camp site... all they will smell is your stinky human body. Bear canisters are only a physical barrier... I do not like putting my food far away from my tent... kinda risky if far from home. My son recently did 1,300 miles on the PCT and used a Bear Vault where required... but he kept all smellables in anti-static bags inside the Bear Vault near his bivy.

Years ago I made some food cans out of metal paint cans and did lots of testing. I watched two bears walk by my tent up in the mountains at Philmont Scout Ranch. They ignored the two full food cans sitting there.... I painted them camo so they looked like tree stumps. Nothing leaks out of a good old fashioned metal paint can unless the lid seal gets dented or rusty. Last year I opened a virgin 35 year DuPont Lucite paint can left over from when I first painted my house. The paint was totally fine. The design of the classic metal pry-off paint can lid is amazing... so simple but delivers a totally hermetic seal. Same with food tin cans. Keep them dry and the beans inside will last a hundred years or more. Because nothing goes in or out thru steel.

Keeping food residue off the outside of your camping food container is very important. I wipe them down with hand sanitizer or stove fuel (alcohol).

Herbert Sitz

Locale: Pacific NW
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 16:54:40 MDT Print View

I think James raises a couple interesting points.

James M. said, " I think it is safe to say that reliance on OP sacks as the first line of defense against bears is probably not a good thing."

Although I'm skeptical of conclusions people seem to be drawing regarding complete inefficacy of OPSAKs, I wouldn't think of (and I don't think many others do think of) OPSAKs as "first line of defense". The _first_ line of defense is the food hang, which if done properly can thwart even bears that know there's food in it. Preventing bears from smelling the food hang is definitely secondary, though I'd like to do it if I can.

James M. said, "If the OP sack leaks, it likely leaks enough to be smelled by proximal bears, black or brown. If the dispersive area drops from (an example only) from say 50' to 25' it would reduce the area in which a bear would detect it by about 2/3, but NOT prevent him from breaking into and eating your food."

James throws out 25' and 50', but I'm curious what we should take to be "proximal" bears. I've questioned conclusions people are drawing because I think by "proximal" we should maybe be thinking several hundred yards, or a quarter- or half-mile. Granted, the BPL test may provide evidence that we might expect bears to smell both OPSAK and ziploc at 25'. But what if bears can smell ziploc contents at half-mile and the comparable OPSAK only at 50 yards? Pretty big difference, and I don't see that the BPL test tells us much at all about that.

A quick check indicates that bear density in Sierras is on order of 0.5 to 1.0 bears per square mile. (California Bear Population) Densest area I've been is Quinault River area on southwest side of Olympic National Park, where density may be around 4 bears per square mile. (Black bears in Quinault Indian Reservation)

What are the odds a bear is going to randomly wander within, say, 100 yards of your food hang? (Perhaps high in some cases, low in others.) Are properly used OPSAKs with food smellable by bears 100 yards away? Is a ziploc with your food smellable 100 yards away? I don't know, but BPL close range test results notwithstanding I would place my bets on the OPSAK being harder for the bear to detect than ziploc at a distance of 100 yards or more. Maybe the distance is more, maybe it's less, would be good to know. (But again since OPSAK is a secondary defense I don't see it as critical to food safety. It's just something that's helpful to a food hang, increases odds that bear won't identify and try to get to your food.)

John Nausieda
(Meander) - MLife

Locale: PNW
Re: Re: Bruce, thanks for the posting about anti-static bags on 04/10/2013 17:23:10 MDT Print View

The steel paint can sounds very promising.Super cheap and a great seal. A question remains about how it is lined?I too have old latex which looks good but there is O2 in there when half full. Is it BPA free? Do the plastic cans that hold wallboard compound work as well? Has anyone cooked in a steel paint can ?

Edited by Meander on 04/10/2013 17:25:23 MDT.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/10/2013 18:20:58 MDT Print View

"It's just something that's helpful to a food hang, increases odds that bear won't identify and try to get to your food."

Yes, I think we can both agree that smell based deterance is probably not necessary and at best will reduce the "foot print" a food bag or canister will impart to the environment. The first statement was a bit of an understatement laced sparingly with sarcasim indicating reverse logic. Sorry, it was a bust and was not meant to be taken quite so literally.

Well "proximal" can mean many things. To some, it can mean the tent walls. To others a half mile. In this context it is fairly specific. Any distance the bear can detect the odor through the OP sack. It really does not matter what that distance is.

Kevin Flynn
(kmflynn_01) - MLife
Great Study! on 04/10/2013 21:14:16 MDT Print View

I bought a few OPsaks a couple of years ago and after they tore apart while opening them I went back to double bagging ziplocks. I've never regretted it, not had a problem.
I have both bear canisters and ursacks in which I place my zippies - glad to know what I've always suspected - that the opsak/loksaks were mostly hype.

Rick Burtt
(rburtt) - MLife
Nylofume or anti-static on 04/10/2013 21:31:49 MDT Print View

Really interesting article. Beyond the obvious results, my experience with OPSAKs has been negative just based on built quality. I've had seams blow out too often to trust these bags. I bought some nylofume bags that I haven't tried yet and am now considering anti-static bags, but so far I lack any true scientific data. I may do my own experiment with my dog who behaves like a bear - I dare not leave my food bin out unattended or she treats it as her own personal smorgasbord!

scent on 04/10/2013 21:54:00 MDT Print View


But, it doesnt prove or disprove any advantage of odor resistant bags in real situations.

As others said, what is wanted is to reduce the chance of a bear smelling your food 100 yds away, not 5 ft from it.

What you proved, was that there was enough odor from all the bags for the dogs to detect it within the small distance used.

I dont understand odors totally, but I do know this, you dont have to touch something, to leave an odor on it. Odors actually "fall" off objects, this is why a person leaves a scent trail, the person didnt touch the ground, just the bottom of their shoe, but their scent is there.

Following this reasoning, the bags could have easily been contaminated during loading, you just have no way to tell. Just because you didnt touch it, doesnt mean you didnt leave scent on the outside of it at all.

Edited by livingontheroad on 04/10/2013 21:56:05 MDT.

Sam Farrington
(scfhome) - M

Locale: Chocorua NH, USA
odor proof bag tests on 04/10/2013 22:39:58 MDT Print View

A couple years ago, I posted on GEAR a comparison test of Opsac and Ziploc bags in real woodlands with real wild critters, over several weeks time. The difference was stark.

The results were confirmed by use of Opsacs for unmolested trekking caches, and info about that was later posted also.

So now we have this article that purports to have some modicum of scientific reliability, and finds there is little difference. As Joe Biden said, "Malarky."

These were trained, domesticated dogs, not real wild critters.
Heaven knows what kinds of odor training they had already been exposed to.
Who knows what kinds of food might have been stored by students previously in the lockers.
The dogs were not given an opportunity go after the 'protected' food to see what else might have attracted them.
As already noted, no empty bags were used as controls.

Something done in the outdoors away from civilization, in areas populated by bears and other wild animals, for subsantial periods of time, and with the animals having an opportunity to get into the 'protected' food, would be useful.

Long story short, a good test for our purposes would simulate real life conditions and events as much as possible.

What really got me is that my scientific training is nil, yet despite the expressed reservations of a few, there is the oohing and aahing from members, many of whom have plenty of scientific training and should know better. (No names, you know who you are.) It raises the cosmic question: Can you rely on a dam* thing you read on the internet.

Good. Now I feel much better. Don't respond with angry posts, as I'll waste no more time on this thread; but should you really want to unload on me, feel free to PM, and I promise to read, maybe even respond after I cool off. Good hiking to you.

Edited by scfhome on 04/10/2013 22:50:43 MDT.

steven franchuk
Re: scent on 04/10/2013 23:05:59 MDT Print View


But, it doesnt prove or disprove any advantage of odor resistant bags in real situations.

As others said, what is wanted is to reduce the chance of a bear smelling your food 100 yds away, not 5 ft from it.

What you proved, was that there was enough odor from all the bags for the dogs to detect it within the small distance used."

Keep in mind that a bear doesn't need to use his sense of smell to find your camp. Many people follow established trials and campsites. Over time the bears will learn where those sites are. If they learn that people carry food then they will frequently visit esablished camp sites in the hope of finding food.

Once a bear is in your campsite the odds of him finding your food go up simply because he is closer to it. Furthermore the more you handle your food the greater the chance you will move the smell from inside the OP sack to the outside of your bear canister. Even if OP sacks attenuate the smell it won't help if the bear is in your campsite and the outside of the canister smells like food.

Even if you avoid heavily used campsites and somehow found a way to keep the smells in the OP bag bears can still find your campsite. How? They followed your smell. Bears know what humans smell like and none of us are taking any steps to eliminate our own smells.

So overall no mater how effective or ineffective OP sacks are bears will still be able to find your food. So if there is no way for you to prevent bears from finding your food, the only option left is to make it impossible for bears to eat it. And the only way we have of doing that now is toe use a bear resistant canisters.

so in my opinion the central conclusion of this study:

"The bags tested in this study are not 100% odor-proof as advertised and should not be relied upon as a stand-alone food protective strategy when travelling in bear country."

Is valid.

Dale Wambaugh
(dwambaugh) - MLife

Locale: Pacific Northwest
Re: Re: scent on 04/11/2013 00:02:58 MDT Print View

I've assumed that doubled freezer bags would help to slow down the discovery of my food. There are so many other factors in the field, with handling and associated odors leading my list. Animals learn to associate humans with food and we are walking odor factories, with soaps, deodorants, smelly feet, plastics, leather and a thousand other things we might have with us.

Bob's moth ball story is interesting. I have wondered why a repellent hasn't been developed, but it would probably be nasty for humans if it would deter a hungry bear.

The electric fence idea makes a lot of sense to me as it adds negative reinforcement to the mix. I think an electric version of an Ursack would be great and adding some electric charge to a bear can would add to creating negative associations with food and people. I would love to watch a raccoon grab an electrified food sack. It begs to have an indicator LED and remote control. A wire mesh electric bag for a backpack could be handy too.

Rob Lee
(roblee) - MLife

Locale: Southern High Plains
Re: Re: Re: scent on 04/11/2013 02:37:36 MDT Print View

Ari developed an interesting question, designed a simple pilot study to test under controlled conditions, all within constraints of time, money, and availability of subjects, handlers, researchers,and facilities. The results are simply presented to the intended audience with scientific vigor, and the experiment could be easily repeated to test its validity. Oh, and he did it on his own dime and the officers (both canine and human) received some free training. A few assumptions by me, but likely a high probability it was close to this scenario. His conclusion was not overreaching: "The bags tested in this study are not 100% odor-proof as advertised and should not be relied upon as a stand-alone food protective strategy when travelling in bear country."
Very practical study and practical/useful advice. Surf and Dale provided a good start on several variables that can lead Smokey to your stash well before he smells it. I'd add an additional small list: hearing you, seeing you, seeing your camp, his hunger level, good health status allowing him to forage far and wide and fast, breeding status, his level of aggressiveness,presence of cohorts that might exacerbate the situation, and how importance that particular spot of his territory is to him. A tip of the Sunday Morning Hat to you sir! And to those who responded with a sense of gratitude for the service you provided us and to those for whom this piqued a spark of wonder and curiosity. I'm looking forward to the foil bag test and any other of the fine challenges that a well crafted study always generates.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Re: scent on 04/11/2013 04:19:26 MDT Print View

I think that our good experimenter made the articles point. That is, OP sacks don't work as a primary defense for food. Reason dictates that you should NOT sleep with them, ever. Secondarily, was that dogs, could smell scents through them, though dogs were only a means, not the actual target of the study. Like heating a flask in lab, using a bunsen burner was not the point of the experiment, though it also proved the burner worked.

Scent, like vision to you and I, appears to be a primary input to bears, dogs and cats. I suspect this also means there is specific qualities that we cannot detect. Like the amount of food available, overall shape of the scent source, direction, and other things we are unaware of. We can debate this to some degree. Dealing with our lack of fundamental knowledge in this area is perhaps another science in it's own right, and, while mentionable here, should not be debated, here, though.

Since the real life target was bears, I would quibble that the experiment should have used bears for better relavency, but, dogs work as well given the testing parameters: easily mobilized, easy to handle, not dangerous and usable within the constrained budget & time. No doubt, there would be quibles about individual animals if it had been done with bears: caged/wild/jaded/etc. Generally, a well done experiment with provable goals. Personally, I tentativle accept the results with the caveate that repeated testing would include a blind target, ie, one with nothing in it to remove all sources of possible contamination.

As far as techniques to maximize food safety and personal safety (albeit indirectly,) these debates do not effect the experimental results. We can debate the merits of various techniques freely. Ryan Jordan, et al wrote of electrical bear bags a few years ago, I think. Canisters are pretty well established, though often derided. I hate to carry the d@mn things, myself. Hangs and techniques are a normal part of camping. Electric fences are well known, but, usually avoided due to weight and complexity concerns. Metalic skinned films have been known for many years, since the latter 60's when they discovered dissappearing water in fallout shelters *through* plastics. I am sure there are others...

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: scent on 04/11/2013 09:14:19 MDT Print View

After the fact, you can always come up with differences in an experiment that might make it better. You have to decide on something, do the experiment, publish results, repeat if you want.

The fact that the dogs found some and didn't find others, with about the same number for regular bags and "odor proof" bags, puts a huge question mark on whether odor proof bags are effective.

And the fact that no experiments were found that showed effectiveness.

Ron Bell
(mountainlaureldesigns) - F - M

Locale: USA
OP Saks Work OK in the Field on 04/11/2013 09:38:04 MDT Print View

While many things in the article are inferred - but not proven - from this one non outdoor test as it relates to backpacking in the field - remember that there there exits a fairly large body of practical user experience and reports OP Saks working very well in the field in backpacking settings.

I find this broad and direct backpacking user information a FAR more compelling a reason to continue to use them as one important part of a safe food carry and protection system. I know I feel safer with my food in an OP Sak and then rolled inside a thick cuben dry bag vs anything else short of a full bear canister, and like most all lightweight backpackers I'm not planning to carry one of those except where required or in special cases.

Disclosure - we do sell OP saks at MLD, but it is a fairly low profit item - in fact we hardly make any money on them as many orders are for only one set of the bags- not much profit after all the order processing and shipping handling, stocking , etc for a fairly low cost item.

The following quote is from Ryan Jordan, backpacking light owner from the BPL product page from when they were sold in the BPL Store a few years ago.


" Are O.P. Saks Really Odor-proof?
Well, yes, quite so. We slathered a bunch of honey, peanut butter, and olive oil in one and left it out for four days in the corner of a forest service cabin while we were out tramping around on a hike. We knew the cabin to be infested with both mice and pack rats, and when we came back, the O.P. Sak was intact with no sign whatsoever of animal intrusion, despite the fact that there were fresh droppings and sawdust scattered throughout the cabin.

Ursack liners are actually O.P. Saks. And, we've been using O.P. Saks for food storage while backpacking in both grizzly and black bear country in Glacier NP, Yellowstone NP, the Bob Marshall Wilderness, Tetons, Wind Rivers, and Uintas. Below the treeline, we simply add a mesh sack with a drawcord and hang our food with AirCore Plus. Above the treeline, we store the O.P. Sak under a pile of rocks, or sometimes, just sleep with it next to our shelter. Even in the most rodent-and-bear-infested areas, we've not had a single curious critter attempt to get into the O.P. Sak. "

Edited by mountainlaureldesigns on 12/16/2013 16:16:23 MST.

Michael Tauben
(mtauben) - MLife

Locale: My heart is in the hills
No surprise on 04/11/2013 09:51:46 MDT Print View

These types of studies on subjects many people people would never even think about is why I have alway loved BPL.

Anyway this came as no surprise to me as I have been backpacking with dogs for years and have used OP sacks for both my own and my dogs food and believe me the dogs know exactly what is in the bags and know when meal or snack time has arrived. I still do use OP sacks, however, I have come up with a system where I put all food in ziplock bags first, so all food residue stays in there, and then put multiple zip bags in one OP sack. This does not really cut down on my dogs ability to smell the contents but means everything is more secure against moisture, bugs, rodents and other issues. It also extends the life of the OP bags so I can use them over and over again. I also always use the PCT hang method.

I think another interesting issue here, however, is the subject of keeping bears away altogether. We are in their territory when we are out in the wild and should never forget that. We either except the inherent difficulties of that or we don't. By the way, ironically enough, the most effective way at keeping bears away is to have a dog with you in the backcountry. You guys at BPL should ask Justine/Trauma, about his experiences with his dog Yoni. There is more than enough anecdotal evidence to support this idea, and could make a good study topic for BPL. But to me it is a fact and just another great reason that all land in this country should be opened up for responsible dog owners to enjoy with their best four legged friends.

Greg Mihalik
(greg23) - M

Locale: Colorado
Re: OP Saks Work OK in the Field on 04/11/2013 09:56:34 MDT Print View

"While many things may be correctly or incorrectly inferred - but not proven - from this test as it may apply in the field - there exits a fairly large body of practical user experience of with OP Saks in the field. "

Sort of like the anecdotal experiences and folk lore about water treatment and giradia.
Stories are nice, but I like science.

Mary D
(hikinggranny) - MLife
Similar test, opposite results! on 04/11/2013 10:02:15 MDT Print View

While this article is interesting, it completely contradicts the test I did several years ago with my own dog, as reported in detail on page 2 of this thread. (I'm surprised nobody has commented.) My dog easily smelled his kibble from several feet away through two layers of freezer bags and started to tear into them. With the food in an OP sack, he either walked by or took a quick sniff and walked away. That's quite a difference!

I never have and never will rely on OP sacks to be effective against bears (OK, that's the same conclusion as the article), but at least with the OP sacks, I could turn my back on my food without worrying about my dog's getting into it! My dog clearly demonstrated that OP sacks are definitely more odor-resistant than two layers of freezer bag.

Basically, the article only demonstrates that OP sacks will not keep specially trained dogs out of "controlled substances." How about testing with food? If you have a dog of a hunting breed (retriever or scent hound), freezer bags, an OP sack or two and some odoriferous dog kibble, try your own experiment!

As a dog owner, I would caution against relying 100% on the dog handlers' statements about their dogs' abilities. We all think our dogs are perfect--dogs do inspire that kind of love!

Edited by hikinggranny on 04/11/2013 10:09:29 MDT.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Similar test, opposite results! on 04/11/2013 10:22:50 MDT Print View

You could do an experiment with bears - leave out a number of OP sacks and regular bags, spread around in a wild bear area and see which ones get broken into - but then you would be teaching bears to eat human food so you would never do this.

I agree, controlled substance trained dogs is a difference from reality that makee the results questionable.

Richard Nisley
(richard295) - M

Locale: San Francisco Bay Area
Re: Similar test, opposite results! on 04/11/2013 10:31:24 MDT Print View

In 2006 I asked a dog trainer to test OP Saks for me and he came to a similar conclusion to Mary's. His forum post was as follows:

paul johnson
(pj - M) SUBJECT Re: OP Sac Test Request - Please ON 06/08/2006 00:27:20 MDT POST REPLY


I've tested it with my sole remaining dog. Well, actually, my wife's new puppy. Like all growing pups, he's a real "chow hound".

I've tried both cheese and peanut butter, and his favorite bacon scented chew (the bacon scent is so strong, i can smell it faintly just entering the kitchen.

First, the pup is placed upstairs out of "earshot". The pup, just 5mos old, already associates the sound of all types of noise related to plastic bags with food.

Then, a two person assembly job. I never touch the foodstuffs or chew. She doesn't contact the zips. My wife places each of them in a Glad zip-lock bag. Then, each of the two zips are placed in an O.P. Sak purchased on the BPL website some many months ago.

O.P. Saks are placed in dining room. Pup eventually finds them as he wanders about (plastic odor??? or serendipity???). The pup is curious, sniffs, and ignores the O.P. Saks.

Now the Glad zips are removed from the O.P. Saks and placed in a freezer sized zip-lock bags. The test is repeated. Bags are placed in dining room.
Pup finds the bags and bites at the bags.

Need to do the test in this order since a dog (and most animals), when it comes to food, can learn to associate (probably not a memory in the human sense of memories, hence the term association) from a single exposure/experience. That is, to be a little clearer, if the test is done the other way around, a dog, the pup in my case, would be attracted to the O.P. Sak simply because it had already learned or associated food with plastic bags.

Richard, i've had dogs for years and though an amateur have much experience training dogs - both mine and friends. I would also kennel friend's dogs at my home, where they all would receive some obedience training even if that wasn't the purpose for the stay.

Training for my dogs consisted of on and off lead obedience, out-of-sight whisper commands like used with sentry dogs in Viet Nam, protection, tracking, and now therapy-dog with my wife's new puppy which she's already using with her oncology patients to keep their spirits up while they are getting chemo.

In the field, co-worker didn't use O.P. sack. He hung his food. I didn't hang my food (no bears, but a lot of rodents). My food in plastic bags inside of O.P. Sacks - actually tripled bagged - yeah...i know...perhaps overkill. His tent, pack, and plastic storage bags were all bitten through by a bold nocturnal rodent raider to get to a candy bar - still in wrapper - that he forgot was inside of his pack. My gear and food untouched.

As far as i'm concerned O.P. Saks work.

Note: A friend of mine an ex-USAF and long-time professional dog trainer (IMHO, the best i've ever encountered) has many Shutzhund competition dogs and a large clientelle. He has stated that next to him, i was ("was", not "am" - it was about 20yrs ago he said this) the best dog trainer he knew in the State at that time - he was probably being kind and was exaggerating. I use something akin to the Koehler method which is staunchly based upon an understanding of canine psychology as the proper foundation and basis for all canine training. Just "Google" Bill Koehler is interested - amazing credentials. Most public libraries have one or more of his four books.
Edited by pj at 06/08/2006 01:12:30 MDT.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
Time for diffusion on 04/11/2013 10:42:24 MDT Print View

Richard and Mary,
Thanks for the feedback. It was be interesting to see those tests repeated (ideally with more than an n of 1) , allowing 24 hours for the food to sit in contact with the bags.

Mary D
(hikinggranny) - MLife
Dog testers on 04/11/2013 12:08:55 MDT Print View

Does anyone have a pack of beagles or foxhounds or bloodhounds to replicate this experiment with food using several scent hounds? Of course, each dog needs to be tested separately so the pack mentality doesn't affect the results.

Richard, I ran my trials using the doubled freezer bags first. It didn't make any difference. After the first trial, my dog did investigate the OP sack, but walked away after a single sniff. In all trials the dog was in another room while I got things ready.

Ike, the kibble had already been in the single freezer bags for 2-3 weeks. It was because I could clearly smell it myself when walking into the room that I became concerned. I was afraid that if I could smell it that clearly, my dog would attack his pack! I ran the trials two days in a row, so the second day the second freezer bag and the OP sack had been in use for about 24 hours. A week or two would have been better. However, in the field three weeks later, my dog showed no interest until the kibble packages came out of the OP sack at feeding time. Nor did he sniff around his pack during the trip, or during subsequent trips.

Ben Pearre
(fugue137) - MLife
Science! on 04/11/2013 13:51:51 MDT Print View

Wonderful work!

This test shows that the bags are permeable to the "illicit" molecules to the point that there's easily enough scent for a trained dog to detect at close range, because the search times are similar. Right? Or does the fact that there were DNFs suggest that the dogs are close to their perception threshold?

Are the times taken by the dogs similar to times taken to find un-bagged goods? That would suggest that (a) the bags do nothing or (b) the times taken are not a great measure of effectiveness.

I'd be curious to see whether bags decrease detection range or probability or etc, and this study doesn't do much to convince me that that won't happen--it defies common sense (but then, so do the data on bike helmets; I'm willing to be told that my common sense is wrong). But then, I haven't encountered many bears--do they just come to where the humans are and then nose around? Or do they smell food from far away? If the former, then perhaps this experiment is more valuable than if the latter?

And how about non-bears? It can be useful to avoid attracting other critters. Does this experiment show that bags won't help there either?

Scott Toraason
OPSA:K on 04/11/2013 14:11:53 MDT Print View

Where were the OPSAKs obtained for the study?

Bill S
Re: Opsaks on 04/11/2013 16:36:09 MDT Print View

In bear avoidance, I would distinguish between avoiding *detection* due to scent, and minimizing attraction due to the same. What this study shows is it's almost impossible to avoid detection.

Even if you want to quibble with the details of the study, it should remind us just how *extremely* sensitive a bear's nose is. When you're dealing with an animal that can smell food--or even the tiniest food residue-- from miles and miles and miles away, isn't that kind of daunting and humbling to any effort you might make to conceal your food's scent? Once you really start to think about everything we touch during a typical day--even a day of hiking--you pretty quickly come to the conclusion that you're covered with food residue.

No matter how careful you are, you've gotten something food-like or smellable on you, surely, at some point during the day. All it takes is a speck. Just touching food and then brushing your hand against your bag or yourself an hour later would be enough to register a scent at this level of sensitivity. So it's just not realistic to expect that you'll defeat the bear's nose. It's just not. In my sleeping bag in the woods at night, when I think that I am really just making myself feel better.

Most bear avoidance strategies take two approaches:

1) Reduce the scent you're giving off to make yourself less attractive to the bear.


2) Physically prevent the bear from getting to your food in some way. e.g.,, bear bag it, put it in a canister.

If you're being realistic, you don't spend too much time worrying about 1.

Almost all of us smell like food when we go to sleep in the woods, but only a few of us have bear encounters at night or otherwise because of it. We don't know if that's because there's a certain threshhold we crossed--because we smelled *too much* or because of some other opportunistic factor. A lot of the objections to the study argue that there's a threshhold level of smell, and that OP sacks help you avoid that threshhold. To me the jury is still out on that after this study. We still don't know for certain if the OP sacks help you *smell less*, and if that makes any difference. The dogs may have smelled the OP sacks as quickly as the ziploc bags because they were both giving off enough of an odor to make them easily and straightforwardly detectable by a dog's super-nose. But that doesn't mean the OP sack isn't less odorous at a very granular level--and it doesn't tell us if that level of difference might make the bear less inclined to wander into camp.

All I know from my own experience at this point is that why we have bear encounters at night is always somewhat mysterious, because I know that I always smell, but only once in a while do bears wander in to check me out. So ultimately I have to rely on (2), creating a physical barrier to my food, in order to assure it is safe. If what I am really worried about is getting killed by the bear once it wanders in to camp for my food, (2) won't help me with that, but assuming I survive the encounter and the bear doesn't defeat the protection system, I'll still have my food in the morning. In part, the intense interest in the topic is probably because we're afraid of bears, period, and avoiding detection is so important because it assures us we won't have an encounter in the first place.

Edited by pnchike on 04/11/2013 16:47:40 MDT.

Stephen Barber
(grampa) - MLife

Locale: SoCal
Dogs, bears and mice on 04/11/2013 16:42:06 MDT Print View

What this study shows, bottom line, is O[dor]p[roof] Saks . . .


bags on 04/11/2013 20:58:12 MDT Print View

Im not sure the study shows anything conclusive. It suggests something, for sure. But further work would be warranted.

Personally, I am quite sure none of the bags are 100% odorproof, I would call any claim to such as false anyway. All plastics are permeable, to some molecules, to some small extent. It is only a matter of time and concentration.

That said, it is very unexpected that simple ziplocks would be statistically no better than more impervious plastics. This does suggest some problem with the testing protocol.

Not to mention that illicit drugs, are not the same as food. Different chemical species involved. Entirely likely that some chemicals are more able to permeate the plastics than others. Perhaps the drug of choice contained a particularly aggressive permeant for the bag material.

There was no control that proved that the loading process did not contaminate the outside of the bags.

The assumption seemed to be made that the only way to contaminate the bags with the odors of the illicit substances, would be to actually touch them with something contaminated.

Not true at all. Odors are vapors, humans can smell ppm quantities of certain things. Dogs can smell quantities so small, we cannot fathom it. The finest scientific instrument cannot even begin to approach a dogs nose.

Simply having odor resistant bags in the vicinity of the samples, even while loading, could have contaminated the outside of them all to the point the dogs could detect them all.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: bags on 04/11/2013 21:01:38 MDT Print View

Nylofume plastic bags are used by the termite tenting industry. It is impervious to the lethal gas so that food can be left within a tented home without contamination. However, they tell you to double-bag your food, just to be safe. If it keeps lethal gas from getting in, then it ought to be good at keeping food scents from getting out.


Stephen M
(stephenm) - MLife

Locale: The Deep Frreze
Re: Re: bags on 04/11/2013 21:15:35 MDT Print View

Fair point Bob.

obx hiker
(obxcola) - MLife

Locale: Outer Banks of North Carolina
nylofume and mylar anti-static bags on 04/12/2013 09:52:11 MDT Print View

The anti-static bags are really interesting. Anyone know of a way to purchase a few bags instead of a case....or want to form a co=operative effort to buy a case? In the cause of science?

Since my aged human nose is obviously the least reliable scientific instrument known to mankind I'm sure you should take the following with several large grains of salt; but here goes.

I've used the opsaks for years and seal them very carefully, yet have noticed a food aroma upon opening my bearicade. I also generally tend to ziplock bag my food, then separate it into meals and days and bag the days inside small 6/gal trash can liners. then all this goes into the opsak.

My last Sierra trip I doubled bagged with nylofume. The nylofume bags have what I believe is a much more reliable and less likely to fail double sealing process of twisting the bag by twirling it about a hundred times and tying off; then twisting the part above the tie again and tying off again. I also bend and tie the 2 ties together. It's easy and fast, doesn't require a smooth flat surface to meticulously press the opening closed and much less prone to user error than the opsak closure. Due to the thin nature of the nylofume you can put a REALLY tight twist on the bags. No testing but it's hard to believe water could penetrate a tightly wound and twice tied off nylofume bag. I suppose I ought to try sinking a bag closed by this method in the tub under water.

There was no detectable odor when opening the bearicade with the food bagged in the nylofume.

BTW the nylofume will not give at ALL. You should squeeze out any extra air before closing it or it will easily burst if pressed down into the bearcan. Learned the usual way..... ;)

PS: Just remembered another observation that lead me to doubt the efficacy of opsaks. I've tried packing them with clothing, sitting on the bag and sealing it to try and make a vaccuum seal. Air always gets in. Maybe That could be a fast test on the nylofume.

Edited by obxcola on 04/12/2013 09:59:49 MDT.

Daniel Fish

Locale: PDX
... on 04/12/2013 10:16:17 MDT Print View


Edited by on 06/09/2013 22:02:19 MDT.

Scott Toraason
OPSAKs on 04/14/2013 13:11:27 MDT Print View

The manufacturer does not claim that OPSAKs are 100% odor proof, that being said the disclaimer hidden below the glowing Backpacker Magazine endorsement for OPSAKs on the their site. However I would agree that the intent of the manufacture is to imply that OPSAK's are odor proof.

No mention is given where the OPSAKs were obtained for the test; I would assume from an authorized dealer. Be that as it may if the OPSAKs were obtained from Amazon or eBay then they are assumed to be defective as posted by a warning on the manufacturer's official website.

(drown) - F - MLife

Locale: Shenandoah
Re: odor proof bags may still do some good on 04/14/2013 13:36:33 MDT Print View

Bears are drawn to human camps by human scents. Once there they scavenge for food. It makes no difference if your OPsak doesn't smell from a mile away, you do, your camp does, and if a bear has leaned to associate those smells to easily obtainable food it will come scrounging around your camp and OPsak or not it will find your cache and your head if your using it as a pillow. Yikes!!!

I use an Ursak or Bearikade always, unless hiking where there are no bears.

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
re: OPSAK on 04/14/2013 15:49:00 MDT Print View

@Scott- The OPSAKs were purchased online from REI at our expense for the purpose of this study. They arrived sealed in the manufacturer's packaging. I had no reason to suspect they were defective, but after the surprising study results, I individually leak tested each one by inflating with air and compressing them.

I appreciate all the constructive comments. These will help to strengthen future efforts in this area. We hope to begin our second study within the next month. It was intended to be directed more towards law enforcement concerns, but I hope to re-examine some of the findings from the pilot study using more dogs and a number of other odor-proof options. We will also incorporate a negative control (odor-proof bag with a scent packet held over the open mouth of the bag and then withdrawn, leaving the bag empty). This should help to address concerns about dogs targeting some feature of the bags other than the scent contained within, as well as contamination of bag exteriors with scent.

Hopefully at the end of all of this, we will also have enough bags left to do a small scale (e.g. 12 bags per group) in situ study with both positive and negative controls.

Luke Schmidt
(Cameron) - MLife

Locale: The WOODS
Re Re Opsak on 04/14/2013 16:26:08 MDT Print View

"We will also incorporate a negative control (odor-proof bag with a scent packet held over the open mouth of the bag and then withdrawn, leaving the bag empty). This should help to address concerns about dogs targeting some feature of the bags other than the scent contained within, as well as contamination of bag exteriors with scent."

Have you considered just bags that have never been near drugs? I know dogs are trained to look for actual drugs but in the absences of that could they be looking for plastic bags since the two often go together?

Also would it be possible to do a test in an open area to see how fare away the dogs detect drugs in Opsaks, in ziplocks bags, and with no bags. This would answer some of the questions about whether Opsaks help if a bear is farther away.

Willie Evenstop
(redmonk) - F

Locale: Greater Yellowstone Ecosystem
How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/14/2013 16:29:07 MDT Print View

Do the police have an interest in showing the bags to be useless for concealing drugs from their dogs. ?

I think that is going to bias the study.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: odor proof bags may still do some good on 04/14/2013 16:30:55 MDT Print View

Yeah, that is pretty much how I feel. But, this is not a scientific finding.

I tend to think that bears do not like human body smells, generally. We stink to many wild animals. (Sometimes, I can even smell myself after a few days of hiking in hot sun up in the peaks area. I agree, I stink.) There is nothing scientific about this and *may* offer a hypothesis, or pre-hypothesis conjecture with more refinement and study. Maybe it drives most bears off. Hard to say.

Lets face it, Dr. Jutkowitz is the ONLY study I have seen on this subject. There are a lot of "if's, but's, maybe's surrounding what was done. The scientist is perfectly willing to correct any errors that come out of a public review, do it over including corrections, and, expand it. Well Done, indeed!

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/14/2013 16:33:27 MDT Print View

If the bags were totally effective at blocking odors, then the police would not want to advertise that fact to potential drug smugglers.

If the bags were totally ineffective, then the drug smugglers would read that and move on to some better method of blocking odors.


Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Re: odor proof bags may still do some good on 04/14/2013 16:35:48 MDT Print View

"We stink to many wild animals."

Well, a black bear does not exactly smell like a rose.

I've been told that the only thing worse than the smell of a bear's body is the smell of a bear's breath.


Gary Dunckel
(Zia-Grill-Guy) - MLife

Locale: Boulder
Vacuum sealing on 04/14/2013 17:54:11 MDT Print View

Ike, I very much appreciated reading your study, and it opened many of our eyes to the reality of conrolling odors in our food supplies. The extensive discussion that followed has been interesting as well.

One thing stood out as curious to me, however. You indicated that the controlled substances were vacuum sealed, and then covered with some sort of canvas, right? I was astounded that the vacuum sealing didn't form a definitive barrier through which odors couldn't penetrate. Is it at all possible that the exterior of the vacuum sealed bags, or the canvas itself, had been contaminated by the handlers when they packaged the controlled substances? Or had the dogs possibly become conditioned to detect the smell of canvas, and not the drugs at all?

I would be very interested in some type of similiar study that involved actual odiferous food (not drugs or canvas) in vacuum sealed Foodsaver bags, to see if food smells can actually penetrate those bags.

All in all, it was a good study, and the results/conclusion seem in fact valid. Thanks for doing this for us, Ike.

Bradley Danyluk
(dasbin) - MLife
Bear attacks on 04/15/2013 10:15:40 MDT Print View


It seems to me that the purpose of proper food storage really has nothing in common with the goal of preventing an attack.

The goal is to keep a bear from stealing your food. That's about it.

Attacking humans is an energy-expensive and risky move for a black bear (even grizzlies only seem to do it defensively).
From what I've read, black bears will very occasionally attack campers inside a tent at night. But these are basically exclusively predatory attacks by starving or deranged bears. Very little to do with stealing your food (even if you kept your food in your tent, it seems to me much more likely the bear will knock down the tent, take the food and run if that is its goal - why bother attack you, unless you try to get in the way?) There are definitely incidental injuries and deaths that occur this way, but I tend to view them not as an "attack" but as a heist mission gone bad, where the thief is forced to maim (or accidentally kills) the guard.

The most dangerous attacks are the ones where the bear's goal is *you*. In that case, it really doesn't matter where your food is or how meticulous your campsite is.

Certainly people should make sure that they are not deluded into believing that proper food storage makes them safe from bears. It makes your food safe from bears... big difference.

Edited by dasbin on 04/15/2013 18:34:26 MDT.

steven franchuk
Re: Odor Proof helps but isn't a comprehensive bear strategy on 04/15/2013 22:48:44 MDT Print View

It seems to me that the purpose of proper food storage really has nothing in common with the goal of preventing an attack.

Daniel, If you look at wikipedia list of fatal bear attacks you will find that none came from Yosemite even though Yosemite bears constantly raided campsites for decades looking for food. When a bear walks into a campsite looking for food they don't want to attack people. Attacking people is just as dangerous to the bear as it is to the person. Most bear attacks o are related to cubs being nearby or when a bear feals threatened by a person. Others atacks have no explaination.

It is well known that yousemite had a lot of bear problems. The bears managed to find way, to get hanging food sacks most of the time. If you were not garding your food there was a good chance the bear would get it. Bears even learned how to break into cars to get food (usually causing extensive damage to the car). That was the past.

Today Yosemite requires all backpackers carry a bear proof canister. The bears quickly learned that they couldn't get into the canisters. Now most Yosemite campers never see a bear. They may walk through the camp at night, but as soon as they see the canister they move on. The bear proof canister is sized so that a bear cannot carry it away. Canister are size so that a bear cannot carry it in its mouth and a bear cannot carry it in its paws.

"to me, the best way to insure the next day's meals is to keep your food with you while you sleep."

Storing food in your tent is the worst thing you can do. That attracts the bear to your tent and increase the chance of bear person encounter. The beast way to insure you have food in the morning is to use a bear proof canister. The only way your food can disappear at night is if another hiker opens your canister steals the food (which has probably happened).

Edited by Surf on 04/15/2013 22:54:17 MDT.

Clayton Mauritzen
(GlacierRambler) - F

Locale: NW Montana
Re: Bear attacks on 04/16/2013 05:50:08 MDT Print View

Bradley, this contradicts the vast majority of research on bear behavior. According to Stephen Herrero (Bear Attacks: Their Causes and Avoidance), most of the predatory grizzly attacks that we have recorded in the Lower 48 and in Canada were caused by bears that had been conditioned to human food. Once bears begin to identify humans as a sources with viable food, their fear of humans and boldness near them increases dramatically, and this leads to much greater chances for a violent encounter. Thus, food storage is an essential component of bear management, especially with grizzlies.

I suggest that you read the above book and corresponding research before recommending courses of action fundamentally in conflict with well-established knowledge.

Edited by GlacierRambler on 04/16/2013 06:23:09 MDT.

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Re: Bear attacks on 04/16/2013 14:46:39 MDT Print View

I think you guys need to seperate the discussion into two areas. One is the black bear, and one is the brown bear (grizzly). Those are two completely different animals and they behave differently.


Bradley Danyluk
(dasbin) - MLife
Re: Re: Bear attacks on 04/16/2013 15:34:27 MDT Print View

"most of the predatory grizzly attacks that we have recorded in the Lower 48 and in Canada were caused by bears that had been conditioned to human food."

I can't disagree, having not read that particular book, but my own reading led me to believe that predatory grizzly attacks are a small fraction of bear attacks. Even within the realm of grizzly attacks, most are defensive in nature. Black bear attacks are generally not defensive (they and their cubs tend to just tree themselves when threatened) but a wide variety of abnormal aggressive behaviour which may or may not (likely not) have anything to do with scenting food.
My point is more that, while there are a lot of black bears out there after your food, they tend to be the less-violent sort who are will go after the low-hanging fruit first (the stuff they can get without a fight, that is). There are also a fair number of curious/aggressive black bears interested in *you*, it seems - which has not so much to do with your food.
I've read of a couple cases of predatory grizzly attacks, but they seem to be extremely rare and in nearly every case the bear is starving or injured. I haven't read about this particular link with food scents you mention - it seems a bit odd to me as they tend to devour their victims, which I would suspect is a much greater source of food than what you're carrying.

Edited by dasbin on 04/16/2013 15:35:42 MDT.

Clayton Mauritzen
(GlacierRambler) - F

Locale: NW Montana
Re: Re: Re: Bear attacks on 04/16/2013 19:40:53 MDT Print View

Bob--agreed. In fact, their behavior is dramatically different. However, proper food storage is still an essential component of managing each species.

I don't want to take the thread drift too much further, but I feel that this point does need to be made. It gets to the heart of the OPSak issues.

Tom Clark
(TomClark) - MLife

Locale: East Coast
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/17/2013 06:32:04 MDT Print View

I'm in the food packaging industry, and just saw this timely article touting a new aroma barrier bag by OdorNo. The company website offers no insight concerning the technology used or data to compare with other options, but I thought I would mention it for consideration. However, the more I read about the little that the company actually says it leaves a bad taste in my mouth.

Here are some quotes from a separate article...

"Not even a dog can smell through my bags," said the colorful Fortune, between laughs and smiles as he demonstrated his product's effectiveness."

" has already begun to order them from us,"

Daniel Fish

Locale: PDX
... on 04/17/2013 07:32:37 MDT Print View


Edited by on 06/09/2013 09:25:20 MDT.

Clayton Mauritzen
(GlacierRambler) - F

Locale: NW Montana
Re: Thanks for the recent comments on 04/17/2013 16:43:43 MDT Print View

Daniel, it's an excellent one--the gold standard for the issue. FWIW, I also found the author very easy to interact with. I emailed him about a question I had regarding his research, and he replied back within a day or so.

Gary Dunckel
(Zia-Grill-Guy) - MLife

Locale: Boulder
Herrero's book on 04/17/2013 16:54:27 MDT Print View

Daniel, I concur with Clayton's opinion. Steven Herrero is probably the most preeminent expert on the griz. His studies seem very scientific and well designed. Also, his writing is quite readable. For further info about the brown bear, check out the Craighead family. They were pioneering griz studies in Yellowstone (and Glacier) back in the 60s-70s. They were also scholars, being based at the University of Montana. They have been a bit controversial, but they did a good deal of valid research. There are numerous books about the griz, but Herrero and the Craigheads pretty much stick to science, with little anecdotal conjecture thrown in.

Edited by Zia-Grill-Guy on 04/17/2013 17:50:40 MDT.

Ian Clark
(chindits) - MLife

Locale: Cntrl ROMO
Great read on 04/18/2013 00:03:55 MDT Print View

I enjoyed your article and I appreciate the time and effort you put in to the project. I don't enjoy bear encounters when I am in camp. Even a cat circling my camp at night can get me a little edgy. I think I have been lucky, but not all have been so lucky and this is in a state with no Grizz. Just because someone did not die in their tent from injuries from a black bear encounter and make Wikipedia does not allow me to take the critters for granted. Congratulations on generating a flurry of comments and I look forward to reading more of your articles.

Jennifer Mitol
(Jenmitol) - M

Locale: In my dreams....
Odor lessenining?? on 04/18/2013 07:29:41 MDT Print View

It may not prevent a bear from getting my food, but wow they do a great job of keeping ME from smelling the hot n spicy cheez its in my entire pack and on all my gear.

aluminum foil on 04/18/2013 17:52:31 MDT Print View

Lots of food and other items seem to be supplied in packaging with aluminum foil liner as well. I have always figured that cut down on permeation.


I made the mistake once, and only once, of putting a bit of toothpaste in a tiny ziplock.
Everything in my pack smelled like toothpaste, like the ziplock wasnt even there. It was horrible. I can say, ziplocks are super duper permeable by comparison.

peter vacco

Locale: no. california
Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/20/2013 19:52:20 MDT Print View

nice article.

it has been my experience that peanuts will stink directly thru a ziplock, but cashews and almonds will not display anything like that sort of thing.

tide laundry detergent will also go right thru its bag, and into MY food.
the stuff from trader joe's does not do that nearly as much.

story :
once upon a time outside of jasper alberta i chanced to buy a whole large packet of pepperoni, which i soon opened and rebagged. it was Good and Hot pepperoni, and once opened you could smell it not only outside it;s bag, but outside the pack !
omg... so .. i ate it.
ALL of it.

it burned going down. and it burned going out.
yee haw !


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: How Safe Is Your Food? Investigating the effectiveness of odor-proof bags on 04/21/2013 00:44:14 MDT Print View

Here in Oz it used to be traditional - like dead normal, that all gear smelt of sausage. Instant tribal ID.


Texas Chinooks

Locale: DFW
Re: Re: Odor Proof helps but isn't a comprehensive bear strategy on 05/08/2013 18:44:02 MDT Print View

Well, I guess I'll use a bear canister so I don't train the bear but honestly I probably smell like everything that I'm storing. I brush my teeth with smelly toothpaste, I probably wipe my hands on my pants or food smell is transferred to my walking sticks, the wrapper to my Pro-Bar is in my pocket until I stop for dinner and put it in the trashbag in my bearikade, the steam of my cooking meatloaf is probably in my wool shirt.

Michael Ray
(topshot) - MLife

Locale: Midwest
Impressive K9 on 05/17/2013 20:39:51 MDT Print View

This local story reminded me of your testing. I wonder if it's really smell they use for phones or (ultrasonic) sound? To smell it while inside a ziploc under water is quite a feat.

Curtis B.
(rutilate) - MLife

Locale: Pacific Northwest
Great article! on 08/07/2013 20:16:01 MDT Print View

I know I'm playing necromancer in reviving an old thread, but this was some might good research work!!

David Erikson
( - M
A different opinion on 08/18/2013 13:21:19 MDT Print View

I've used OP sacks for the last 10 years (at least) in the Sierra Nevada backcountry on annual trips. They were used in conjunction with an Ursack as final protection. On at least 4 occasions when bears were IN OUR Group's CAMPSITE the bears failed to detect the food I had; my food was taken by me as a supplement to the group's food. The latter was stored in aluminum panniers ("bear boxes" if you will) used now by all mulepackers in the Sierras. So it might have distracted the bears from detecting my food, since there was no attempt to conceal the contained food's odors, as I did with the OP Sacks. On many other occasions there was no evidence or knowledge of a bear's presence during the night, but we were in areas notorious for bears along the John Muir Trail, such as at or near Thousand Island Lake, Lake Ediza, Glen Aulin, (and ALL other sites on the Yosemite High Sierra Camp Loop), Rock Creek (Cottonwood Pass region), Cottonwood Lakes, Rae Lakes, Paradise Valley and other sites on the Rae Lakes Loop (this included one of the episodes of a bear in camp attacking the aluminum bear boxes but ignoring my stash) or East Lake. Indeed, I've not had my stash moved at all suggesting a bear had tried to get the food but gave up. I might add that my food was always some distance away from the aluminum boxes containing the group's food, which I would think would lessen the "distraction" factor sited above.
So the bears ain't got my food yet.
David E.

Luke Schmidt
(Cameron) - MLife

Locale: The WOODS
Re A different Opinion on 08/18/2013 14:19:41 MDT Print View

I definitely felt like my Opsack did a better job of containing food odor then regular ziplocks. It made me feel a lot better in grizzly country.

I've read that bears actually have pretty good eye sight so I work under the assumption that if the bear is close enough to see my bear bag he'll probably investigate whether he can small it or not. I try to rig my bear bag in a place that is not super visible. In the feature I'll probably take a stuff sack for my bear bag that is either camo or a low visibility color like brown or gray. I don't want an orange sack that sticks out like a sore thumb.

My theory is that an Opsack is better then nothing especially if a bear is a couple hundred yards away and he hasn't seen my food bag or my shelter.

David Erikson
( - M
"odorproof" OP Sacks vs black bears on 09/04/2013 16:11:55 MDT Print View

As a follow-up to my posting above: I just spent 4 consequtive weeks in the Sierra Nevada backcountry with my OP sacks concealing my food against bears and other wildlife. Nary a nibble; on the other hand, there was no evidence of bears being in the vicinity, or at least no obvious bear attempts on our camp food which was stored in aluminum bear boxes carried by mules. Also, the frequent presence of mules may well have kept ursines away.
David E.

Trace Richardson
(tracedef) - MLife

Locale: Southern California
Second Study on 02/16/2014 08:18:50 MST Print View

Anyone know if the second study that Ike mentioned ever occurred?

Ike Jutkowitz
(Ike) - M

Locale: Central Michigan
Re on 02/16/2014 12:44:17 MST Print View

Sorry Trace. Dealing with some personal stuff at the moment. It's on the back burner for now, but I'll keep you posted.

Wayne Koepp
(arky82) - M

Locale: Northwest Arkansas
How Safe Is Your Food on 08/13/2015 08:34:24 MDT Print View

I would think that masking the odors would be more effective than trying to contain them. You could try something like powdered sulphur or spray a Ursack with OdoBan Bitter Barrier. I know our cat takes one lick of the Bitter Barrier and never returns.

Anthony Britner
(ant89) - F

Locale: North Wales, UK
Scent proof? on 08/16/2015 09:07:59 MDT Print View

Plastics are actually porous to scent particles so they can escape by being absorbed into the plastic and then released on the other side the longer the scent is in the plastic container the more scent diffuses though.

However metal containers are not porous so scent particles cannot diffuse through it can only excape at the joins/ openings.

Thickness of material comes into the equation. The thicker the material and/ or the more layers there are then the longer it takes for the scent to diffuse into the outside air.

It may be possible to mask the scent of the food by including a very strong smelling, potentially displeasing substance in one of the outer layers.

Mitchell Ebbott
(mebbott) - M

Locale: SoCal
Closure Type on 08/16/2015 21:02:08 MDT Print View

I'd love to see a test that includes Nylofume/Nylobarrier bags, or even the BaseCamp bags that you can get at Amazon or WalMart. These bags are made to be closed with the twist, fold, and twist-tie method, and that seems a lot more secure and odorproof than the zip on the OPSack.

Jennifer Mitol
(Jenmitol) - M

Locale: In my dreams....
then why don't drug smugglers use them? on 08/18/2015 17:15:18 MDT Print View

I mean, if there truly were a plastic ziploc bag that masked odors from dogs (which are way less blessed in the olfactory department) why in the world wouldn't they be the hit of the drug smuggling community?

That's all I have to say.

Mitchell Ebbott
(mebbott) - M

Locale: SoCal
Re: then why don't drug smugglers use them? on 08/18/2015 19:14:51 MDT Print View

How do you know they aren't?

Ken T.
(kthompson) - MLife

Locale: All up in there
Re: then why don't drug smugglers use them? on 08/18/2015 19:56:21 MDT Print View

Because turkey bags are cheaper. Local favorites method.