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My scumbag opsack is now putting out an odor! :-P
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Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Bags on 08/26/2013 15:19:58 MDT Print View

"Debating things that are obvious isn't interesting to me. Please just read the Loksak website. They explain that Opsaks are made of polyethylene, including this sentence: “These resealable, washable, polyethylene bags are watertight, airtight, and odorproof, so they prevent animals from sniffing out your edibles and toiletries.""

You piqued my curiosity, so I followed your recommendation and did some reading over at loksak.com. Here is what I found: "Our new Odor-Proof barrier bag, OPSAK, has all of the features of the aLOKSAK PLUS A NEW-GENERATION BARRIER FILM THAT IS COMPLETELY ODOR-PROOF."

I capitalized the relevant phrase for the sake of clarity, as it is apparently easy to overlook. The clear implication is that the OPSAK is composed of 2 layers, one polyethylene, and a film made from an undefined(proprietary?) odor-proof material.
This would certainly seem to at least partially explain Samuel's results. This is not to say OPSAK's are the best choice, by any means. I gave up on them last year, as soon as NyloBarrier bags became available, primarily because of the finicky, unreliable zip lock sealing mechanism.

Colin Krusor
(ckrusor) - M

Locale: Northwest US
Material on 08/26/2013 16:10:41 MDT Print View

Tom, the implication you inferred from that quote is not as clear to me as it is to you, but it would be interesting if it came to light that Opsaks are a multilayer film. The Opsak material is soft and subjectively it appears to be a monolithic polyethylene film. So, if it is a multilayer film, it is a pretty safe bet that it doesn't include a PET (polyester) or PA (nylon)layer (which are "hard", crinkly, low elongation materials). The only "soft", high elongation materials I know of that are used in barrier films are PVA and PVDF. PVDF, however, is naturally a milky, translucent color when dry (it turns clear when wet), and Opsaks are clear. That leaves PVA.

As long as we're on trivia, I'd note that even a multilayer film will never match the barrier properties of metallized and foil bags. Small molecule permeance for foil bags is typically 1000x lower than the best multilayer clear films. This is why some barrier bags are metallized on one side and clear on the other, or even metallized all over with a small clear window; companies want buyers to see their product but they want to maximize the proportion of the bag area that is metallized in order to minimize permeation of oxygen, water, and odor molecules.

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Material on 08/26/2013 17:02:45 MDT Print View

"Tom, the implication you inferred from that quote is not as clear to me as it is to you, but it would be interesting if it came to light that Opsaks are a multilayer film. The Opsak material is soft and subjectively it appears to be a monolithic polyethylene film. So, if it is a multilayer film, it is a pretty safe bet that it doesn't include a PET (polyester) or PA (nylon)layer (which are "hard", crinkly, low elongation materials). The only "soft", high elongation materials I know of that are used in barrier films are PVA and PVDF. PVDF, however, is naturally a milky, translucent color when dry (it turns clear when wet), and Opsaks are clear. That leaves PVA."

Not to be overly disputatious, but when they say "plus" a new generation barrier film(definition: a thin skin or membranous coating) it sure seems to indicate another layer is involved . I suppose the best way to resolve the issue would be to email the question to loksak, but I'm not sure I'm that interested in pursuing the subject further. As I mentioned earlier I'm no longer using OPSAK's, so this discussion is purely theoretical for me. As for the rest of your post, given your use of words like "subjectively" and "it's a safe bet", I'm left to wonder if perhaps there have been advances you are not aware of in the materials you mention that would alter their textural properties. Or perhaps there are even new materials you are not aware of. They did say "new generation" after all.

"As long as we're on trivia,"

The devil, as ever when it comes to the real world, is in the details. As any scientist is well aware ;0)

I'd note that even a multilayer film will never match the barrier properties of metallized and foil bags. Small molecule permeance for foil bags is typically 1000x lower than the best multilayer clear films. This is why some barrier bags are metallized on one side and clear on the other, or even metallized all over with a small clear window; companies want buyers to see their product but they want to maximize the proportion of the bag area that is metallized in order to minimize permeation of oxygen, water, and odor molecules."

A multilayer bag construction involving a film doesn't have to match the barrier properties of a foil/metallized bag, although in the absence of data driven comparisons I'm not inclined to accept your statement as a given. All it has to do is fool the bear. There are probably several ways to skin this particular cat, one of which is no doubt metallized bags, but another of which may well be some form of multilayer bag with an odor proof film. BYOB would seem to be the order of the day.

Steven Adeff
(TinCanFury) - F

Locale: Boston
LiteTrail NyloBarrier "seconds" on sale! on 10/14/2014 07:54:28 MDT Print View

http://litetrail.com/collections/sale/products/litetrail-nylobarrier-pack-liner

"seconds"

Also, my personal OpSak test with my, and a few friends dogs resulted in essentially the same results as the BPL test. They could smell the difference, with new bags, and especially more used bags, between the bags with the treats they love vs their standard dog food.

All this said, regardless of how odor permeable the material is, the outside of the bag will end up taking on a smell, your bear bag itself will take on a smell, etc. So what you are doing is not attempting to prevent any smell from emanating, but to minimize the smell to where the bear will decide to go to other smells first, or not be able to smell it from the distance they happen to be. At that point, they will smell your body well before they will smell the bag. If they decide to approach because of your smell, they will find the food regardless of what you put it in.

Bags like this just buy you one more level of comfort so you can sleep at night, they don't buy your food 'bear invisibility'.

Samuel C. Farrington
(scfhome) - M

Locale: Chocorua NH, USA
Odor Proof Bear Bags on 10/14/2014 22:28:58 MDT Print View

From earlier in this thread: "So next spring, when our bears come out, I will return to the small clearing in the forest behind the house and see how the Nylo bags do next to the Ziplock freezer bags used before."

OK, so this is what happened. First, please note that nobody sent me any suggestions, protocols, or the like. If you do PM me, please include an email address if you'd like a reply - my PM service receives but does not send.

Three bags were hung on April 7th, when snow was still on the ground, at the same forest clearing used before. Dark olive nylon bags from Walmart were used for hanging. The food used was birdfeed, "Wild Berry Treat" consisting mostly of suet, and some canned salmon and canned sardines. The food was placed inside 3 freezer pint Ziploc bags. One Ziploc was placed inside an Opsak, one inside a Lite Trail Nylo Barrier Odor Proof Bag, and one remained naked. The Opsak, Lite Trail and naked Ziploc were each sealed and placed inside one of the 3 nylon bags. Here are pix of food stored only in a naked pint Ziploc, and in a pint Ziploc placed in a sealed Opsak. The pix were taken later after final removal of the contents from the nylon stuff sacks:
Opsak&Ziploc-Contents

On the left is the food in a pint Ziploc, stored in a medium Opsak with a Clip'n-Seal cllp, and on the right is the food stored in a naked pint Ziploc. There is no picture of the Ziploc pint bag and food that was stored in the Lite Trail bag, as that was 'taken.' However, the Lite Trail was twisted tightly shut and tightly secured with each of the two twist ties provided, an inch or so apart from each other.
(No instructions came with the Lite Trail bags.)

The bags were hung from tree limbs approximately 50 feet apart, all with the Walmart nylon bags as an outer cover. After several weeks - nothing. After several more weeks - nothing. So on May 15th, the bags were moved to a more remote location where in the past, hunters had placed a bear stand for several seasons. The snow was long gone by this time and ticks abounded.

The three bags were hung 75 to 100 feet apart, and suspended about seven feet high from branches 25-30 feet high that were judged too light and springy for a raccoon or the like to walk out upon and pull up the cords. The area was accessed from a nearby game trail, identified by moose and coyote tracks often seen when snowshoeing. The Lite Trail was closest to the game trail, but at least 100' from it, the Ziploc around another 75 or so feet away, and the Opsak another 100 feet or so away. The distances are only approximate and were not equal, as the primary goal was to find high hanging branches that would support little weight, but would not break, and they were scarce.

Several more weeks passed. We're in early June now. Nothing. So the bags were lowered to five feet. One June 21st, the nylon bag containing the Lite Trail bag was found on the ground ripped open, with the Lite Trail bag ripped apart, and the Ziploc containing the food was gone without a trace. Here's a pic:
LiteTrail-remains

The Opsak bag, furthest from the game trail, was also found on the ground, with the cord cleanly severed right at the top of the outer nylon bag; but there was no sign of damage to the nylon bag, and the Opsak, Ziploc and food inside were untouched. The nylon bag containing the naked Ziploc with the food, that had been hung between the other two bags, was found still hanging, apparently untouched, still at five feet above the ground. Here are pix of the nylon bags containing the Opsak and Ziploc bags after they were recovered:
Opsac&Ziploc-Undamaged

At this point, I felt not much could be made of all of this, so retrieved all the bags. The odor from the naked Ziploc bag was strong and foul, and could be smelled right through the bag. Not so with the Opsak. The torn remains of the Lite Trail bag was all that was left in its nylon outer bag, and the Ziploc with food was gone without a trace.

But I did draw one conclusion and a couple surmises form the above. First, I would not trust a Lite Trail bag. Also, I do not think bears were involved, and suspect coyotes were at work. We know they are around because they make quite a racket celebrating after each kill. And I would think bears would have done more damage to the nylon bag containing the Lite Trail. Lastly, I don't think the survival of the naked Ziploc shows much, as the Ziploc inside the Lite Trail bag didn't help it much, and the naked Ziploc stank when retrieved. Of course, you are free to draw your own conclusions.

A little daunted by all this, I have been in contact with an acquaintance who works at a bear shelter, and am hoping to obtain some more reliable tests of the bags next year. Next time, I will probably double bag, as that is what I do when using the Opsak bags for caches. (Note: The Opsak bags now come in a larger size that better fits the clip'n-seal clips.) If anyone has any suggestions about protocols, I remain open to them. Possibly, the bags could be placed well apart from each other on the tops of a bear enclosure to see if any bears are attracted to them. In that way, the bears would not receive the food, with the negative consequences that might entail.

Thought you might be interested, so there you have it. Sam in Chocorua.

Edited by scfhome on 10/14/2014 22:41:07 MDT.

William Chilton
(WilliamC3) - MLife

Locale: Antakya
Re: Odor Proof Bear Bags on 10/14/2014 23:10:33 MDT Print View

Thanks for going to the trouble of carrying out this test, Samuel.
Unfortunately, it would seem that the test has failed, since the control bag was untouched, so we can't really conclude anything from it. The fact that the Opsak bag was uncompromised COULD be that the animals were disturbed before getting at the food.
Incidentally, the nylofume bags are supposed to be used double bagged (for fumigating) and I would suggest anyone doing further testing try them double bagged.

Tom Kirchner
(ouzel) - MLife

Locale: Pacific Northwest/Sierra
Re: Re: Odor Proof Bear Bags on 10/15/2014 17:56:50 MDT Print View

"Incidentally, the nylofume bags are supposed to be used double bagged (for fumigating) and I would suggest anyone doing further testing try them double bagged."

+1 SOP for me in the backcountry.