A good alternative to WPB gear for ACTIVE backpacking

[Richard Nisley]

In a related thread Bob M. said, “The simple fact is that even if wearing a mythical shell that is both waterproof and has 1:1 vapor permeability you still have to face the very real physical challenge of ‘pushing’ perspiration (creating enough internal heat to vaporize it so that it passes through the membrane) from one extremely high humidity environment into another.
When there is zero humidity differential this isn’t going to happen and nothing is going to change the physics of this scenario.”
The physics calculations are slightly different because vapor pressure is a function of both humidity (secondary) and temperature (primary). Assuming you have average skin temperature of 95F, then the vapor pressure differential will still push the moisture outside your garment until the ambient temp is also 95F. For a more typical scenario, assume the outside temperature is 60F and it is 100% RH on both sides of the fabric; the driving force would still be a respectable ~38.6 hPa or .2 PSI.
The primary issue with conventional WPB fabrics for backpacking is that in order to be rainproof, the water vapor transport, not the driving force, is of necessity too low to prevent uncomfortable moisture build-up. For an example of this phenomenon, reference Will Rietveld’s excellent 2012 3-part WPB article series where he field tested the most air permeable WPB products available. My physics calculations clearly show me that the only way he could have avoided the uncomfortable moisture build-up in his test scenario:
• wear an outer shell that was not rainproof because it would require a CFM of at least 11.1 CFM with an unventilated backpack
• or 7.6 CFM with a trampoline backplane
• or 7.6 CFM with no backpack.
For those who have no interest in the why and only want to know how: for cold rainy backpacking, a shell with >300mm HH, vs >1,200 to be rainproof, in combination with appropriate polyester under layer(s) for the temperature generally results in significantly less internal moisture build-up than conventional WPB ensembles.

[Mole J]

Yep

Paramo Clothing

http://www.paramo-clothing.com/

 

 

 

[Brad Rogers]

I would guess EPIC would do a great job on the move.  Too bad there aren’t many lightweight choices.

[Stumphges]

Richard,

What would be the minimum permeability needed with ventilated/no backpack and two pit zips open?

[Daryl and Daryl]

Richard,

If I “wear an outer shell that was not rainproof ” I can see how it would reduce internal moisture build up.

But this non-waterproof  outer shell will let in rain, right?

Haven’t I just traded one problem for another? In either case I’m wet.

[James holden]

if youre going to do the non WPB shell method … a FUZZY and FLUFFY fleece is best …

something like a polartech thermal pro …

and yes you will get somewhat wet either way …

;)

[Woubeir (from Europe)]

The idea that you can get wet seems to horrify people. It shouldn’t. As long as you don’t get cold, it shouldn’t be a problem.

I’ve been wet numerous times, both on dayhikes as on multiday/week trips and it was no problem at all.

[Greg F]

From a heat transfer perspective aren’t you better off keeping the cold water on the outside and the warm sweat on the inside?

im think the warm water that get pushed out from inside and the cold water being leaked in creates more heat loss than forcing the heat to transfer across the WPB layer.

Essentially I think you will have small chains of water conducting heat instead of the much lower heat transfer coefficient of the plastic layer.

 

i could be completely wrong here though.  I’m thinking 5-10 C degree weather outside in the rain

[Bob Moulder]

 

The vast majority of the time you’re still going to get wet.

(Unless one refuses to think of very damp as wet, insisting it is dry. Whatever.)

I do recall, however, that a couple of years ago when I hiked in WV I spent 3 days hiking in on-and-off (but mostly ‘on’) very light rain and drizzle, with temps in the low 50s F and was surprised at how well I fared with a Montbell Dynamo windshirt over a polyester base, sometimes with some 100-wt fleece also under the Dynamo. I was still damp, but only a little, and warm.

 

[Eric Blumensaadt]

I don’t like the sound of this “…you’re going to get wet.” thing. But from sad experience I know it’s absolutely true.

That is exactly why, on an unstoppable rainy day I stop and make camp. I am for “short suffering, not Biblical long suffering.

[Woubeir (from Europe)]

I don’t like the sound of this “…you’re going to get wet.” thing.

Eric, that’s what I mean: it sounds worse then it often is. With the right skill-set, it is not as bad as it sounds. Actually, sometimes I hardly notice it.

[kevperro .]

All we need is an ultra-light dehumidifier with a long extension cord.

In all seriousness…. just embrace getting wet.   We need to change the way we think about being in the outdoors.    Rain gear is to keep you warm, not dry, and think about clothing that you can manage your body temp under various conditions and how you are going to stay warm once you reach camp.    Also how you are going to dry wet clothing in camp.

This “staying dry” thing is just a fallacy,  a pipedream.

[Roger Caffin]

Personally, I have come to the conclusion that the whole WaterProof Breathable concept (that it can keep you ‘dry’) is fatally flawed. Both theory (the laws of physics) and practice (30+ years of field failures) tell us it doesn’t work – at least in heavy rain.

So I suggest we update that meme to:
‘You are going to get wet, but you can still be warm’

Cheers

[James Marco]

I agree. WPB clothing is not for keeping you dry. They just keep you warm while getting wet. I usually hike in a long sleeved wool base layer down to about 40F. Sometimes adding rain gear if it’s windy. Yup, I get wet. At the end of the hiking day, I strip it off and wring it out well.

[kevperro .]

The single best thing about breathable rain gear is that once you get wet it has the ability to allow you to dry layers of clothing underneath at the expense of body heat.

If you live in the outdoors and you NEED to dry your clothing that isn’t a bad thing.   It just isn’t something the average consumer is going to appreciate because most never see that situation.   They go home or they take off their wet layers and hang them over guy lines in camp in the fruitless hope that they will dry in a high humidity cold environment.

[Roger Caffin]

The single best thing about breathable rain gear is that once you get wet it has the ability to allow you to dry layers of clothing underneath at the expense of body heat.
ONLY if the surface of the fabric does not wet out. If it does wet out, you lose the ‘breathable’ bit completely.

Trouble is, they ALL do wet out eventually. (And a lot of the DWR treatments are turning out to be toxic.)

Cheers

[kevperro .]

I’m talking about once you get under cover.   The surface of the fabric will dry.    At that point, you can push moisture through it with body heat and dry your clothing given enough time and calories.

It isn’t always a pleasant experience…. but if you want to maintain your clothing you dry it when/however you can.    I’ve lived in <40 deg wet weather for weeks on end and that was the only way to dry your clothing.   Same with our bivy sleeping bags that were Gortex covered.    You could eventually dry them with body heat.

[Roger Caffin]

Same with our bivy sleeping bags that were Gortex covered. You could eventually dry them with body heat.
The GoreTex shell craze passed some time ago, when it was realised that the down will dry MUCH faster with a plain fabric shell rather than a vapour transport inhibiting membrane. It turns out that air flow through the fabric carries a a lot of water vapour out: air flow due to body movement.

Goretex shells are of some value in igloos where there can be a lot of water dripping. Doubtless other similar situations exist.

Cheers

[Stumphges]

If we’re resigned to using WPB gear to dry out/get warm at rest/at camp, then it seems DriDucks – which is almost as breathable as any WPB fabric, can’t wet out and costs $20/set – might be the best thing going. In camp, the fragility of the polypro material is a non-issue. Wear some heavy fleece under and it will allow body heat to steam out damp layers without the worry that prolonged rain will tamp down the hydrophobic tails of toxic fluoro-DWRs.

[kevperro .]

This was a military issue bag.   It was some kind of ancient synthetic with about an inch of insulation… and whatever flavor of Gortex shell they had in the late 80s.   It worked…. you could lay in a ditch in the rain and survive… at least I did.    I thought that thing was magic but perspective has a lot to do with it.   I never actually was “comfortable” or “warm”.    I just didn’t go hypothermic and once it stopped raining you could dry it with your body heat over the next couple days.

[Roger Caffin]

Hi Stumpy

A fair argument, except that you WILL need something to keep the cold rain and the wind (serious wind-chill factor) off you sometimes. To be sure, in summer rain we often skip the rainwear and get wet, but when it is 4 C you need a rain/wind barrier. Dri-Ducks is fine until you run into heavy scrub or sharp rock.

At those sorts of low temperatures, any sweat you give off is very likely going to condense on the inside of the rainshell if it is not utterly permeable , so you will still get damp. All you can do under those conditions is try to keep warm – it’s all that matters after all.

Could you wear Paramo-style clothing at 4 C in light-to-moderate rain? Yes, provided you are moving and creating heat; then it works well. But in a serious downpour you will likely need to move to something like silnylon, as really heavy rain can over-whelm the best of Paramo. (A sad combination of high-pressure water and surface dirt overcoming the surface tension factor.)

It may be worth noting that Paramo has been developed for UK conditions. I have lived there for some years and walked there, and for the most part I don’t remember experiencing what I call really heavy rain. All-day light rain and other miserable conditions – you bet!

Cheers

[Richard Nisley]

The Buffalo and US Special Forces active clothing ensembles have UL backpacking equivalences. All three systems move moisture out of your clothing better than conventional WPB systems when active at a typical UL Backpacking pace of 7 MET. All three systems require a WPB while static. For static use, the UL  WPB never has to deal with pack strap abrasion or bushwhacking.

[Richard Nisley]

Mole,

Buffalo / Paramo / etc. were the inventors of this concept. Natick Labs adapted it and then refined it as part of the US Special Forces PCU ensemble. The challenge to this forum is to determine if there are viable UL Backpacking corollaries. I am of the mindset that there are and I created a straw-man for discussion in my earlier post.

[Richard Nisley]

Brad,

You said, “I would guess EPIC would do a great job on the move.  Too bad there aren’t many lightweight choices.” For bushwhacking in the wet, I think the military EPIC garments are OK since you need abrasion resistance in addition to a permanent DWR. For trail use, there are light windshirts available from multiple sources that can be adapted to a wet weather system. Companion base layers from Polartec are also available from multiple sources. The key to adapting a windshirt is that it test over 300 mm HH. The pre-2013 Houdini only tests 70 mm HH.

[Mike M]

I’ve used a Epic shell w/ a very thin base layer (new Patagonia Lightweight grid Capilene) and sometimes the addition of a lightweight grid fleece (Patagonia Expedition weight) during day long rains with really good results.  These are not deluges, but steady light rain.  The key is that you’re moving and moving rather “crisply” :).

When stopped, throw on any additional insulating layer needed and a WPB over the lot.

[Author]

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