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Pack Dry Times
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Ryan Jordan
(ryan) - BPL Staff - MLife

Locale: Greater Yellowstone
Pack Dry Times on 01/16/2012 17:12:56 MST Print View

I'm soliciting feedback to see if it would be valuable for us to incorporate backpack water absorption capacity and dry times into our standard review analyses.

We've done a preliminary series of "proof of concept" tests, with data output like what you see below.

Please let me know if this is data you would find valuable, and how you might interpret, and use it.





Nick Gatel
(ngatel) - MLife

Locale: Southern California
Re: Pack Dry Times on 01/16/2012 17:18:25 MST Print View

Maybe I am different than most, but I never even thought about it.

Years ago I used pack covers, nowadays I usually wear a poncho or if wearing a rain jacket then a pack liner.

I suppose a wet nylon pack will gain weight, but my main concern is keeping the stuff inside dry.

I don't hike in a lot of rain as a percentage of days, but have been in some real downpours over the years.

Dan Durston
(dandydan) - F

Drying on 01/16/2012 17:27:29 MST Print View

There's obviously more to a packs drying time than the fabric, but it might be quite a bit easier for you guys and still helpful for readers if you just did one article on the drying times for the range of different pack fabrics, instead of for each pack you test.

Recording the drying time for each pack would be the ultimate, but even a one-time article comparing materials would be great.

Pack drying times do affect me, as I often like to sleep with my pack under my feet and I can't do this when a pack is wet.

Edited by dandydan on 01/16/2012 17:31:20 MST.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Pack Dry Times on 01/16/2012 18:08:48 MST Print View

Those are some fancy graphs and some cool data. I hadn't previously thought to get qualitative about, other than regards clothing, but absolutely, a wet pack is a heavier pack. Other things being close, a pack that didn't absorb as much moisture and dried out quickly, ABSOLUTELY is the better pack. So I like your idea of quantifying it.

But. . . . while those are spiffy graphs with lots of data, do I, as a potential buyer/user really care THAT much (and I'm techier than most)? No. I care, but I want the punch line.

How about a "drying half life"? One number which captures how quickly a pack dries. which will be influenced by fabric, weave, waterproofing, details of construction, etc. Eyeballing your graphs, it looks to vary from less then 1.5 hours to 3.5 hours. AND, it correlates to total moisture mass gained. Which is also significant but could also be reported as a single number - a percent of dry weight.

So one approach I see is (with SWAG data):

dry weight: 20 ounces
percent moisture absorption: 82%
drying half life: 2.8 hours

Because that would be an inferior pack, for me, compared to: 22 oz, 30%, 1.6 hours.

If I was paying $200 for that first, "lighter" pack, I'd pay $250, maybe $275 for the second one because of its performance when wet.

And here's another approach, based solely on weights:

dry weight: 20 ounces
100% wet weight: 36.4 ounces (20 oz x 1.82)
weight after 2 hours of drying: 27 ounces (guestimate based on previous data).

I think I prefer the all-weight scheme because that is how we judge other equipment and the price/pain/effort to acheive weight savings. Packs aren't always dry. We ought to consider their weight when wet and factor that into our gear selections.

And not just packs, but tents, tarps, etc. Has anyone EVER put a tent or tarp away (on an early-start, high-mileage trip) totally dry?, I haven't.

And how about clothing? We like to not count clothing to get our "base weight" down, but really we carry that weight just as much as pack weight. AND moisture in our clothing hurts us by cooling us more than a wet pack does.

I think you're really on to something here, Ryan, and I think it is applicable beyond just packs.

Having been on large-budget co-op BODs (in eletrical utilities) I've given some thought to what I would push for if an REI Director (been a member for 34 years now). And (1) muscle-powered sports. That's it. Downhill skiing is NOT a muscle-powered sport. And (2) EVERYTHING in the catalog should be clearly identified with its weight. What you are suggesting is far better than that - and the sort of thing that is wonderful when conducted once by a impartial party and reported to all.

James Marco
(jamesdmarco) - MLife

Locale: Finger Lakes
Re: Re: Pack Dry Times on 01/16/2012 18:46:43 MST Print View

I agree with Nick. Getting the pack wet is minorly important, even here in the north eastern part of the country (where humidty is usually higher than 60%, 'cept in the winter.) I am far more concerned with keeping stuff in it dry. Water resistance, top closure, etc would tell me more, I think. You might have missed some of the data that would make it more usefull, IMHO. Not just weight picked up with wetting, how quicly it dries, but also, how well the water penetrated, and what the age of the fabric was.

Silnylon does well for water resistance, drying time, and weight pick up, but fails with abraision and puncture resistance. Good when new, but not so good when it gets a little older. This suggests an age test to me. Difficult to test reliably or with any degree of repeatability.

Your test seems geard to a single type of fabric. A single non-laminated fabric, such as a traditional pac cloth, was never designed to be very water resistant. Water entered through out the cloth, and, the seams. Dyneema was waterproof only because many (most?) were coated with PU. In conjuction with other cloths, some were fairly water resistant, some picked up a lot of water weight, and, some allowed penetration into the pack body. The newer laminates, cuben/nylon hybrids, may indeed pick up a lot, but retain full waterproofness. A 100% cuben pack will also not allow much, if any measurable, penetration into tha fabric. Drying time would be pretty irrelavent to a cuben pack. Indeed, I am not sure if wetting is actually correct, since it will pick up some weight from rain, but, never actually wets the pack, not to start a symantecs sub-thread.

So, they are independent variables. Something not captured well by simply weighing packs before and after soaking them for some standard time period. My opinion only, but water resistance becomes as important as the water retention and drying time of the material. And all three numbers would be influanced by the number of "typical use days" of the fabric. A simple wet/dry weight doesn't really capture the info that I would want in a review.

Water retention and drying time can be computed as you have demonstrated.

How to compute water resistance? This can be very subjective... Perhaps asking for a general opinion on how to feasably test for this might yield some results. I would suggest simply dunking the pack in a vat of water for some time period (not including the top, of course) and weighing it against a fully wet pack? Of course, this means repeating the measuments, again.

Perhaps something equally simple for an "ageing" test. Say 5 hours drying time in a commercial dryer with a half dozen new 1-3/4" childs blocks would simulate a seasons use? Framed packs/stay stiffened packs/internal framed packs would need to have been removed from the frames, stays and internal frames removed, of course. Generally a lot of time to perform this sort of test, repeating the whole set of measurements, again.

Edited by jamesdmarco on 01/16/2012 19:16:47 MST.

a b
Pack Dry Times on 01/16/2012 20:16:12 MST Print View

This is an interesting thread. I was asked by more than one hiker last spring why i don't use a pack cover in the rain.
They usually laughed at my answer but then thought about it and laughed again!
My answer was: My pack only gains 5 ounces when wet. A pack cover weighs about 5 ounces.
Without a packcover, I only carry the extra 5 ounces of rainwater when it is raining.
I would have to carry the 5 ounces of pack cover all the time rain or shine.
So by not carrying a pack cover at all I save 5 ounces any time it's not raining.
Except of course in the state of Connecticut, where i am convinced it rains perpetually.

Dave -
(FamilyGuy) - F

Locale: Up there
Re: Pack Dry Times on 01/18/2012 12:42:33 MST Print View

I seem to attract rain, snow, and sleet so for me, water absorbtion is an absolute key performance criterion in a pack for me especially given I use a liner and not a pack cover.

You lucky desert bretheren....

Dustin Short
(upalachango) - MLife
Re: Re: Pack Dry Times on 01/18/2012 13:05:20 MST Print View

David, not all of us desert folk are so lucky!

EVERY dang solo trip I do I have been rained or snowed on. This past weekend was the worst with my WPB bivy being far from either WP or B (but for $20 from REI worth still worth it ;).

It took two days for my Osprey Talon to dry out and it weighed a ton when soaking wet.

So yes, water absorption/drying times has moved to the top of my list of pack performance.

David Chenault
(DaveC) - BPL Staff - F

Locale: Crown of the Continent
re: pack dry times on 01/18/2012 17:55:42 MST Print View

Those graphs look great. Give us all the data.

For me, this is hugely important attribute, and one I bet many packs will do horribly with.

First Last
(snusmumriken) - F

Locale: SF Bay Area
Pretty graphs, but not useful to me. on 01/18/2012 19:13:15 MST Print View

I've never noticed my back gaining weight in the rain. Maybe it does, but if I don't notice it probably doesn't matter. So pretty graphs, but not terribly useful.

Ken T.
(kthompson) - MLife

Locale: All up in there
Re: Pretty graphs, but not useful to me. on 01/18/2012 19:19:20 MST Print View

+1 with Kristin.

And it rains a lot where I live. Once it is wet it does not dry until you get home. I just focus on keeping the contents dry.
Good suggestion by Dan on an article about this subject based on different fabrics used.

Edited by kthompson on 01/18/2012 22:35:36 MST.

John Abela
(JohnAbela) - MLife

Re: Pretty graphs, but not useful to me. on 01/18/2012 19:27:57 MST Print View

pretty graphs, but not terribly useful


Eugene Smith
(Eugeneius) - MLife

Locale: Nuevo Mexico
"Pack Dry Times" on 01/18/2012 19:35:26 MST Print View

This data doesn't hold much practical value to me Ryan. I haven't once considered in my pack deliberating, how much water I could potentially take "onboard" in a deluge.

Comfort, versatility, durability, and simplicity are priorities- water retention/dry times? Not so much. A fully saturated pack doesn't affect either category for me, never has, likely never will.

Longterm UV degradation on pack/shelter materials? Now this would be something more relevant to where I live and hike, but even then, hardly worth punching numbers over.

Edited by Eugeneius on 01/18/2012 19:37:51 MST.

Stephan Doyle
Re: Pack Dry Times on 01/18/2012 21:18:17 MST Print View

It's interesting data and makes me appreciate BPL's in-depth analysis that we see in SOTM reports but is often lost in product reviews. I don't know how useful it would be though or how much I'd consider it. Neat, though.

Brian Waichunas
(empedocles) - MLife
How much does it weigh wet? on 01/18/2012 22:37:37 MST Print View

I think this is a super interesting way to approach reviewing equipment. I'd add dry times and weight when wet to tent/tarp and shoe/boot reviews as well.

Edited by empedocles on 01/18/2012 23:53:18 MST.

Sabine Funk
(SabineFunk) - F
Re:"Pack Dry Times" on 01/19/2012 04:54:41 MST Print View

That's a good idea to test that. As some others I haven't been thinking a lot about this.
Like Brian, I think, it's also (or more) important to test shoes.
If my pack gets soaking wet it's not much heavier but wet boots are about the worst thing that can happen to you. I had the experience with my boots when they didn't dry out for ages - cold feet, blisters, ...
So it would be really great to find out how long shoes and boots need to dry.

And you should maybe mention what conditions you had when you tested the dry times. There's a big difference between 100°F in a desert and 40°F or less in mountains.

Greg F
(GregF) - F

Locale: Canadian Rockies
Pack Covers on 01/19/2012 09:28:22 MST Print View

I think that this data could answer the question of should I take a pack cover.

If a pack cover ways 20% of the amount of water you expect to take on then if you expect your pack to be wet for 20% of the time you are carrying it it might be a good idea to take a pack cover.

Depending on how much time this testing takes I am not sure if it would be worth it on a continual basis. It might be more valuable to do it once with a bunch of different materials and post those results rather than pack by pack. That would be asuming that the performance between different packs with the same materials absorb a similar % or weight of water.

Michael Ray
(topshot) - MLife

Locale: Midwest
Re: Pack Dry Times on 01/19/2012 10:29:31 MST Print View

Since I advocate not using pack covers and just use a liner, I think it would be useful to know what CHARACTERISTICS would lead to excessive water retention. That would include fabrics, of course, any coatings they may have, taped/sealed seams, padding choices, etc. Many of these are obvious but aren't necessarily pointed out in reviews. Which manufacturers seem best in this area perhaps.

>There's obviously more to a packs drying time than the fabric, but it might be quite a bit easier for you guys and still helpful for readers if you just did one article on the drying times for the range of different pack fabrics, instead of for each pack you test.

+1 what Dan said. Not sure it's worth it to do it for all packs. Just comment on those packs that may exhibit especially good or bad retention based on the characteristics you find in your research.

I certainly would not want Pack 1 over 3, 4 or 5 in your first chart if that was all I saw. So what was it that made it so bad? Of course, I have no idea of your methodology but I wouldn't expect that it was a 60 L volume and the others were just 30 L. Did you wet them by dunking and letting them drain a few minutes (i.e., fell in the creek) or spraying them down on the outside only (i.e., major rainstorm)?

Dustin Short
(upalachango) - MLife
Re: Re: Pack Dry Times on 01/19/2012 15:33:20 MST Print View

I'm curious why so many think it's pointless. Just because you don't think about pack weights when wet doesn't mean it isn't a consideration. It's almost a case of willful ignorance (sounds worse than intended, I'm willfully ignorant of alcohol stove systems because I like my lightweight canisters). More information is never a bad thing. I'm all for the mindset of "if it ain't broke don't fix it" but traditional backpacking isn't broken yet we all experimented and have moved to lightweight packing or beyond.

Also remember many people choose lightweight backpacking because it allows them to do their other outdoor pursuits more efficiently. Canyoneering in particular considers wet pack weights as a foremost consideration, usually second only to abrasion resistance.

Ron Bell
(mountainlaureldesigns) - F - M

Locale: USA
Re: Re: Re: Pack Dry Times on 01/20/2012 08:39:46 MST Print View

No doubt it will be interesting.

Almost any one aspect of a pack or gear item is linked to others that form the whole amd a ranking or measure of one aspect can create a skewed overall perception of the importance of that one aspect. Example, Torso Collapse, if one pack has .5" more collapse than the next one up the rank does thatt mean it's better? Not if the shoulder straps are less comfortable or the overall pack weight is 30% more than the other.

I've done some wet/ dry tests of our gear over the years.

The base Dyneema X fabric gains about 20% when wet. At first that sounds like a Lot. But figure an Exodus uses only about 1.5 sq yds of that base fabric and so the wt gain in that part of the pack is less than 2oz.

If I totally saturate an Exodus by submersion for a worst case it gains about 9oz weighed after a quick shake off. In regular rain when worn it might be closer ot 7-8 oz. So, if the base fabric is about 2oz of that 9oz, then the rest must be in other parts of the pack that could be called the " Features" The 3d mesh and the webbing is most of that gain, some other gets into the cord sleeves , etc and some of that might not happen in reg rain vs full submersion.

If I wanted to create a pack with lower water wt gain, I would use a sealed type pf fabric, some versions of cuben or VX would work. ( Only a cuben or maybe a very light full spectra weave would match the wt and strenght of the Dyneema X and gain less wt wet ) But that fabric change would only save 1 - 2 oz at most in a 3500ci size pack. Any additional when wet wt saving would have to be by eliminating features, smaller straps, less webbing, no load lifters, less 3d mesh or pading, narrower shoulder straps and waist belts, etc.

Of course, any dry increase of overall weight for a design that then has lower wet weight gain = no gain.

Summary: I don't think anyone should get overly excited about the one aspect of a pack's base fabric abosorbing more or less water vs another- it's not that much - it's mostly about the features and design.