Field Testing Air Permeable Waterproof-Breathable Fabric Technologies – Part 2: Are There Detectable Differences Under Real World Backpacking Conditions?

Chris Townsend wrote: "When the DWR treatment wets out the WPB membrane doesn't breathe as well so condensation build-up inside is greater. But the WPB membrane remains waterproof."

Unfortunately this is false. It is a long-standing claim that originated with Gore and is just marketing, not fact. It has been repeated by so many people so many times that it has become an article of faith, but it just ain't true.

When a WPB fabric wets out due to failed DWR, water *will* leak through the membrane. And it gets worse as the fabric gets folded/bent/worn with time. (It's possible that brand spanking new fabric straight from the factory wouldn't do this but that's hardly relevant to the real world.) I've seen this happen with several different jackets and have tested it myself.

I'd love to see Richard or one of the others here with hydrostatic head test equipment demonstrate this.

Stuart, I'd like to here more about the science behind WPB membranes working in reverse.

Reason being, I've certainly gotten quite damp inside my WPB shell during all-day rain. Problem is, it's rather impossible to judge the source.

In September of 2009 I arrived in the little resort of Stehekin Washington. Having just hiked through three straight days of rain through Glacier peak wilderness on the PCT.
I had never been this wet in my life. All my gear, clothes, spare socks, everything was sopping wet.
I was embarassed and felt I had somehow "failed" even though I had used all the outdoor skills of 18 years of hiking as well as the past 5 months spent walking from Mexico.
It was hilarious when i met up with a large group of fellow PCT hikers and discovered that every single person, despite what they had for rain gear; ponchos, expensive WPB jackets, cheap dri ducks.. every one of us was completely soaked to the bone.
The more seasoned long distance hikers simply used a wind shirt and umbrella.
No, they don't stay dry either. The windshirt gets wet and the umbrella slows the replacement of that warm moisture (warmed by body heat) with the cold rain thats falling.
For sitting around camp the high techery works great.
For hiking all day, everyday, through the rain expect to get wet.
There is a saying among long distance hikers:
The only cure for three days of rain is a motel room.
I am not alone in coming to the conclusion that a simple 99 cent plastic poncho is as effective as any 300 dollar WPB jacket at keeping a person dry or rather less wet during multi day rain.

I don't think that the membrane is leaking. What is happening is that the wetness is body sweat and condensation when the DWR fails. At least this has been my experience.

I don't believe that the total saturation of the outer layer of a WP/B shell (or other item) leads to a reverse passage of water from the outside to the inside. For example, I have several single-walled WP/B tents (from Bibler, ID, and Nemo), and they certainly don't leak through the fabric even when the outside is entirely wetted-out (rain water no longer beads). And what about fishing waders that are constantly immersed in water? They don't leak through the fabric, and are undeniably more comfortable to wear than non-breathable, but waterproof, alternatives.

@David,

I've only ever found one article that explained this in great detail and had lab test to show it, but it was a print article from over 10 years ago. I haven't been able to locate it or any similar reports on the web.

It's interesting to try and find any lab tests that actually support Gore's claim that the wetness you get when the DWR fails in solely from perspiration and not from external water leaking through. I haven't been able to locate a single report that backs their claim. As far as I can tell the origin of the claim is Gore's marketing department.

I will have another look around the web to try and find some science to backup my statements.

I have tested it myself though. A goretex jacket with the DWR well and truly removed (it went through the washer twice with detergent…). I draped the jacket over a bucket and filled the depression with water. And couple of hours later, there was about half an inch of water in the bottom of the bucket. I'm pretty sure the bucket wasn't perspiring :) After a good wash-in DWR treatment, the same test produced no water in the bucket.

I've done this with two other jackets, one gore-tex (>10 years old, had never had its DWR renewed apparently) and the other some proprietary goretex-like membrane. Same results.

Anecdotally, I've had DWR-less goretex let heaps of water through the shoulders with me just standing in the (heavy) rain for a couple of hours – there was no sweating going on (yes, I know about insensible perspiration – it is insufficient to explain the amount of water that got through.)

I'm always surprised when people repeat Gore's claim about this. I just assumed everybody knew it was just spin.

Cheers

@Stuart – your experience certainly suggests that the fabric is leaking. I have had gortex paclite wet out under extreme (rain) duress, but I have not had it leak. I have also had internal condensation that could have been assumed to be leaking through except that the rain was cold and the internal moisture was very warm.

This definitely calls for some scientific analysis by BPL!

Consider that the membrane may simply be overwhelmed with perspiration as well as the shell wetting out and about the same time. The relative humidity is also increasing as the air is saturated after hours of rain— everything is soaked inside and out and the whole system spirals into a soggy mess.

As Matt found out in Stehekin, after that many days of rain, the cold moist air has permeated everything– the air, ground, foliage, your gear and clothing. And you're working hard, hauling your load in steep terrain. There is a real difference in moisture management with hours or days of cold drizzle in saturated landscape vs something like a thunderstorm in an otherwise dry environment.

Could someone explain how a wpb membrane like goretex could "reverse" and let water in?

I am a bit skeptical, as I have used goretex and goretex knock off dry suits and paddle pants while immersed in water and didn't notice any leakage. It would seem if the only thing preventing the wpb membrane from reversing is the dnr coating then I should get wet, yet I don't, as the coating is completely "wetted" out while underwater.

Is it possible that the folks are just noticing that when the surface of the fabric is wet it no longer allows moisture out? Or am I completely missing what people mean by the membrane "reversing".

It would seem like this would be an easy thing to test out..

Great article by the way.

Many thanks for the article and all the interesting comments. Excellent stuff.

I was intrigued by the GoreTex over a bucket test. It's interesting to note that during a hydrostatic head test the outer fabric is saturated yet results can be >20000mmH2O. But here we are talking about leaking over longer time frames.
Could it be that the water from the puddle on top of the membrane is evaporating through the membrane and condensing on the lining? I say this on the basis that condensation occurs not just because of the dew point conditions (temperature, humidity and pressure) but because of the water repellency (surface energy) of the material. The hydrophylic PU layer may have this effect but a scrim lining with washed out DWR would play a similar role.
In the case of waders there's a temperature gradient that may be counteracting this effect and the time scales are different, too.
It's important to realise that water attaches to hydrophobic surfaces, unless they are superhydrophobic, like a lotus leaf (Cassie-Baxter conditions), and that small forces such as gravity or even subtle shaking (of the floor?) may allow droplets to spread out, possibly allowing water to creap through pores in a membrane. This situation can be seen in the lab when droplets on a hydrophobic surface slowly spread out over time.
Alternatively, a simpler explanation may be that the membranes were damaged, physically or by chemical contamination, in all the tests carried out.

Quite right!
I add this comment because it seems to be pertinent to breathability in the rain:
Some people contend that when ambient humidity is 100% no breathability occurs. On the face of it that's true, except where you can warm the air enough for it to absorb some moisture and then wisk it away on a breeze; or in the down wind part of your clothing system where the aerodynamics create a low pressure zone, allowing the air to absorb more moisture than the ambient conditions. So wind and heat loss seem to me to be the key ingredients. But, of course, it's so much easier to get wet than to dry off, and harder to dry in high humidity conditions.
But getting wet's not going to kill you, it's staying warm that's important (thinking: mmmmm, hot bath). By the way, the Blizzard Reflexcell kit provides insulation that is far less effected by water than conventional garments.

As everybody knows here, current WPB technologies are not perfect. Nevertheless today practically only WPB (and may be Paramo garments) provides acceptable function balance in certain areas. Of course we can use silnylon ponchos in lightweight backpacking (i use poncho too), but there are circumstances when we can not. For example mountaineering, canyoning, kayaking, biking. And of course there are backpackers who simply don't like to use ponchos. So it is good to know what WPB technlogy is better. And i think that the main focus of this article is to compare membranes and not to make claim that they all are crap. Besides, technologies are not standing still, progress is good.
It would be interesting for me to make this test with really breathable softwind shells (something like Dryskin or Pertex equilibrium) and with Paramo. Big thanks again, BPL, i can't buy all such jackets to do the tests by myself :) Though it would be fun.

Maybe it doesn't matter whether it leaks or it's sweat

If it's raining, I'll get wet

Plan B is to wear as little as possible, then when I quit hiking it will quickly dry out

I have found eVent and GoreTex to dry pretty quickly when I get out of rain and quit hiking

This is one of the most interesting WPB test I've ever seen. It's a great start to decipher this voodoo technologies.

As Oliver commented, I also think the test is not perfect, but it seems like there is no scientifically perfect method to test WPB jacket so far anyway. Since the temp and humidity is probably not only affected by membrane by itself but also affected by zipper, size and length (also as Oliver mentioned), and the design philosophy of each jacket seems to be a bit different each other, so I would like to see the pure lab test result of each membrane performance exactly in the same lab condition, although the question is what kind of condition is more practical for lab test.

I also would like to see the lab test result of the endurance of DWR and the zipper/seam leakage of the major players.

"Maybe it doesn't matter whether it leaks or it's sweat

If it's raining, I'll get wet"

There are two types of wet. A warm wet, and a really cold wet. Which do you prefer?

I think the amount of water is so small that the BTUs it takes to heat it up are infintesimal, so it doesn't matter whether it's sweat or rain water.

It takes 1150 BTU/lb to evaporate water from 32F

It takes (85-32) = 53 BTU/lb to heat water from 32F (assuming your rain water is 32F just for example) to 85F (which is what I've measured my skin temperature when I'm cold).

Then it takes 1097 BTU/lb to evaporate water from 85F.

So it takes about 20 times as much heat to dry out your clothes, than to heat up them up from cold rain water.

Conclusion – I don't think it makes much difference whether your clothes get wet from sweat or rain, but drying them out with your body heat will make you cold.

I don't think Dave was commenting on drying clothes. He was simply saying it is more comfortable to be warm and damp, than cold and damp, whilst actually hiking.

And safer.

if yr moving youll heat up quickly anyways

as jerry points out … its when yr stopped or moving at a very slow pace when yr effed … the evaporative cooling really takes effect

Yes – Mike simplified what I was trying to say.

I disagree that the net effect is the same. Having been in some incredibly cold rain in temps close to freezing, I would much prefer a little bit of warm sweat to deal with. I would have a base layer on wicking up the sweat and although it is always a challenge to maintain core temps in such conditions, the temperature difference between the sweat and cold rain would be noticeable and the net negative effect on your core temperature would be greater. Any sort of arm chair science aside (and I say this in good humor), my experience suggests otherwise.

I'll have to weigh my clothes when damp and calculate how many BTUs required

And compare that to BTUs required to stay warm

Are you calling me an arm chair scientist? Well, I am sitting on a couch…

I am going to edit that because it didn't come out right. I am the arm chair scientist. And a bad one at that. I can only go by my experience.

Seriously, hiking in near freezing rain is one of the most difficult conditions a hiker can face. Unless you have dealt with conditions like that for days (weeks) on end, it can be difficult to imagine. A oouple of times in the past i've nearly went down with hypothermia. Luckily i wasn't hiking solo at the time. I've had US family come here on vacation, and they have struggled with the weather. I guess folk from the NW of the US and Canada get the same conditions.
Here in Scotland, we do get the occasional high pressure zone in winter. Temps can drop to minus 29C, and the weather is clear and dry. It is pretty simple to deal with conditions like that.

"I am going to edit that because it didn't come out right. I am the arm chair scientist. And a bad one at that. I can only go by my experience."

Don't worry about it, you didn't say anything offensive : )

Anyway, not possible to unring a bell.

It seems to be a consensus that there is no magic with rain shells. It looks similar to waterproof shoes to me, with the industry leaning heavily to the marketing hype.

Okay, assume you will get wet under your rain shell. You stop hiking and there you stand, it is 45F and you are tired and wet and starting to get chilled. Assuming that it isn't pouring, you get a dry layer out of your pack…. but UL principles lean to not carrying spares, or mid layers that might be base-layer substitutes. Oops! Many UL gear lists would have something like a Thermawrap or a light down sweater for insulation, with no spare base layer. I don't like that idea.

This is one of those scenarios where I think light fleece or other stretchy synthetic mid-layers are great. Power Stretch is my favorite, but there are tons of options, from basic 100w fleece to R1, Capilene 2/3/4 and so on. If I have stopped and find my base layer beyond redemption and I am cold, peeling and using my mid-layer for a long stop or camp would be my plan. The base layer might dry if I can get it under cover and a breeze, or a little warmth off a fire if possible. If it isn't soaked it will dry from my body heat– if I don't get too cold trying to do that. Having a second base layer might be in the works too.

My point is that the rest of your clothing should assume that your rain gear isn't going to keep you completely dry, particularly in those scenarios where you are exposed to hours of cold drizzle and high humidity. Remember that long-term cold drizzle equals no direct sun, perhaps for days, so there is little opportunity for drying anything.

What is your solution?

Typical PNW weather: Lake Annette, Washington, July 4, 2010, 2PM PDT, elevation 3600', 49F, 95% humidity. There was a heavy rainfall a couple hours later, followed with hours of light drizzle and cold air from the snow fields above.

Mike Reid wrote about Scotland: "I guess folk from the NW of the US and Canada get the same conditions."

Aye, it is a cool, dewy wonderland :) I think the Scots have more exposed conditions, whereas I can often hide in the trees. You must need some tough tents in Scotland!