/ NEW ARTICLE: Waterproof Breathable Fabric - Explained

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UKC Articles - on 12 Apr 2012
Toby Archer wearing a Neoshell Marmot Zion Jacket, 5 kbIn this detailed article, Matt Fuller and Dr. Mark Taylor explain all the technical details behind waterproof fabrics.

"Making a fabric rainproof is relatively easy. Making a fabric waterproof is really, really hard..."

Read more at http://www.ukclimbing.com/articles/page.php?id=4556

JTatts - on 12 Apr 2012
In reply to UKC Articles:

Sorry to be really boring but if you're going to include an equation, please format it so that it's readable.
Martin W on 12 Apr 2012
In reply to UKC Articles:

Type 2 – Fabrics with microporous coatings or membranes

The picture above shows a microporous membrane up-close

There is no such picture.

Lab tests for water vapour permeability

...lab tests remove the errors associated with human field testing

"Variability" or "lack of control" would be better than "errors" IMO.

Finally, there is no picture of a sweating guarded hotplate as promised in the Complex Methods section. I'm dying to see what one looks like...
garethMottram - on 12 Apr 2012
In reply to UKC Articles:
The only major flaw in the article, which is remarkably accurate for something appearing on an outdoor industry site is in the DWR section. The the assertion that all after care DWR's need the factory DWR to still be present to work is fundamentally inaccurate. It is true of the fluorocarbon based DWR's (e.g. Grangers) and not the silicone/elastomer based DWR's (e.g. Nikwax). It also implied that all DWR's need heat application to effectively bond to the fabric. Again this is not true of the non-flurocarbon based DWR treatments, particularly Tx.Direct.
Generally a very well written and informative article. Well done all!
Goofyfoot - on 12 Apr 2012
In reply to garethMottram: Just a question regarding only wearing a waterproof when its raining hard - I have recently bought a Rab Exodus because it is extrememly breathable and wind resistant (I get very warm when hill walking).

On a recent visit to the Brecon Beacons (avg temp 2 degs,very windy)it started raining but the Exodus more than coped with it - only when it started hammering down did I throw the waterproof on top, at this point my Exodus was wet - how does this effect the breathability of the waterproof hardshell? I'm used to just throwing a hardshell over a softshell when it's required, should I have removed the wet soft shell first?

By the way, very interesting article. Cheers.
charlesr - on 12 Apr 2012
One of the best articles I have read on the subject (but then the authors do know more than most of the people that I have come across): well done UKC for trying to set the matter straight

So much confusion exists because no one test replicates actual usage; hence fabric brands will choose the method that demonstrates their product in the best light

Some people know I work closely with the designers of the garments & we have always used (as a rough rule of thumb) the fact that there are 4 variables: the DWR, the membrane system/ the fabric, the outside conditions & the human. It is worth pointing out that people perspire at different rates on different days (how hydrated are you, et cetera); plus I would question the difference in fabric performance in the UK, the Alps & central Asia as the humidity changes (how close are you to the sea?). With 4 variables you will always get a different set of opinions...

Keep up the good work UKC...
spsmith - on 12 Apr 2012
In reply to UKC Articles:

Thank you.
Mr Fuller on 13 Apr 2012
In reply to UKC Articles: Cheers for the comments. Yes, there are a couple of images missing that have somehow disappeared during formatting, and the equation does look a bit nasty, but I don't think it's impossible to interpret it. Hopefully we can fix these issues.

Regarding the wet layers under the hardshell, it's a quite complex problem. The inherent breathability of the system is reduced by keeping the extra layer on, but the insulation is increased, which may increase the vapour pressure gradient. If I'm soaked underneath the softshell then I usually keep it on and stick a waterproof over the top, though if I'm dry underneath then I'd probably take it off, but this is obviously very dependent on temperature and conditions.
Clive G on 13 Apr 2012 - host81-153-102-248.range81-153.btcentralplus.com
In reply to UKC Articles: An excellent feature and it has generated some random thoughts I would love feedback on.

Putting other factors to one side, sweat needs a certain amount of dry air for evaporation to take place. My memory may be at fault but I seem to recall 5cl of water requires some 850 litres of dry air to evaporate into. So, regardless of a material’s ‘breathability’, given the limited amount of moist air available between your jacket and body for evaporation, water will always be present in its liquid state unless it can be physically lifted and transported away.

This water, and any condensate created by using a waterproof in cold, wet conditions will also adversely affect a material’s breathability.

While this cannot be eliminated, some systems appear better at handling the presence of water liquid and condensate. Paramo will lift liquid from the body and drive it out as long as a pressure differential is maintained and condensate is not present (happy to be corrected here). Keela has a dual membrane system to create a dead area that holds water vapour away from the body until conditions allow it to be transported outside.

As the feature states, lab tests are open for interpretation. Things may have changed since I last looked at this subject but I can clearly remember a major fabric manufacturer testing breathability using desiccant to dry the outer atmosphere to help maximise the pressure gradient and produce satisfactory results. Surely such desert conditions are rarely found when we need to don waterproofs. And I cannot recall any tests yet designed to recreate the body’s true microclimate – although Keela has provided interesting comparison results based around the effects of condensation on its DPS clothing and that using other fabric technology.

Hmm , perhaps it’s time to revisit this and try out a few jackets using the latest fabric technology. Offers anyone?
captain paranoia - on 16 Apr 2012
In reply to Mr Fuller:

Good article, collecting a lot of wisdom in one place; if I looked through all the postings I've ever made on the subject, it might well aggregate to something approaching this article, but I never have... I shall bookmark it and link to it in future, thanks.

I might have spent a little more time on the purpose and necessity of DWR ('wetting out' and the consequences are only touched on somewhat cursorily, whereas maintenance of DWR is pretty essential for a waterproof breathable fabric).
captain paranoia - on 16 Apr 2012
In reply to Clive G:

> My memory may be at fault but I seem to recall 5cl of water requires some 850 litres of dry air to evaporate into.

Without looking up a psychrometric chart, or crunching the numbers, I couldn't say for sure. But the general principle certainly holds; a waterproof breathable fabric will only allow a certain 'vapour flux', and, if you sweat more than this, water will accumulate in your clothing system.

Which is why we generally wear a wicking base layer to absorb the sweat, acting as a reservoir or buffer, and removing the sweat from the skin, making us feel more comfortable. Some base layers will increase the rate of evaporation, due to their complex surface structure which increases evaporative surface area.

The downside of the reservoir effect is that, if the reservoir is large enough, it can cause chilling if the fabric is saturated when high output activity stops (especially if it's a sudden stop). Ideally, we won't run for long periods at high levels of activity, but instead will ramp up and ramp down the level of activity, allowing the buffer to fill and empty without saturating, and without causing excessive chilling.

The downside of wicking is that we remain comfortable so that we may not be aware that we're sweating and overheating, and we delay removing insulation until it's too late, and the fabric is saturated...
DWilliamson - on 16 Apr 2012
In reply to UKC Articles:

Nice one, Matt, glad this is up at last. Regarding the equation, LaTeX is good for typesetting maths and you can even do it online! If I'm reading the equation correctly,

Y_{sg}=Y_{sl}+Y_{lg} /cos /theta_c or
/textrm{Y}_{sg}=/textrm{Y}_{sl}+/textrm{Y}_{lg} /cos /theta_c

should be what you want, except replacing those forward slashes with backslashes (which don't seem to work on this forum). You can use a site like this one to generate an image: http://www.codecogs.com/latex/eqneditor.php
Mr Fuller on 16 Apr 2012
In reply to DWilliamson: Perfect Dave, that first one is bang on. Cheers!
colina - on 18 Apr 2012
In reply to Mr Fuller: ive been wearing a merinio 260 top and a good softshell for some cold days out recvently and to be honest the biggest problem i get is i get sweaty and by the time i get to the summit or whatever i get very cold very quick. the only way i have found to alleviate this problem is to change my merino to a dry garment which as you can imagine is not good stripping off at a low temperature .personally i think all this wicking sweat out moisture out clothing just doesnt work !
captain paranoia - on 18 Apr 2012
In reply to colina:

> and a good softshell for some cold days out recvently

Define 'good softshell'...

If you're getting that sweaty by the top, then your softshell has too much insulation, or your softshell won't let the sweat escape fast enough to keep you cool (a membrane, perhaps?), or you're simply working too hard.

No clothing is magic (not even softshells...); if you're working so hard that you're producing more heat than can escape to the environment, your body will sweat. And if that sweat cannot escape your clothing system, it will fail to cool you down, and you will sweat even more, and the sweat will will saturate your clothing.

So, either you remove insulation until your heat production matches your heat loss (take off clothes), or you reduce your heat production until it matches your heat loss (slow down).
colina - on 18 Apr 2012
In reply to captain paranoia:
> (In reply to colina)
>
> [...]
>
> Define 'good softshell'...
>
> If you're getting that sweaty by the top, then your softshell has too much insulation, or your softshell won't let the sweat escape fast enough to keep you cool (a membrane, perhaps?), or you're simply working too hard.
>
> No clothing is magic (not even softshells...); if you're working so hard that you're producing more heat than can escape to the environment, your body will sweat. And if that sweat cannot escape your clothing system, it will fail to cool you down, and you will sweat even more, and the sweat will will saturate your clothing.
>
> So, either you remove insulation until your heat production matches your heat loss (take off clothes), or you reduce your heat production until it matches your heat loss (slow down).

some good points there,soft shell is a good quality rab at around £100 and the merino at £60.
maybe i am working too hard and need to slow down but thats defeating the object isnt it!
i was only wearing two layers ie a merino and s/shell so unable to take anything off ,difficult to get the right mix of clthing ..too cold to wear just a layer and overheating if im wearing a soft shell.the hunt for the perfect outdoor gear will continue.





Guy Hurst - on 18 Apr 2012
In reply to colina: You might be better off with a simple Pertex windshirt over your base layer. They provide practically no insulation, are very breathable and weigh and cost relatively little. Some would say they are softshells -- and if they are, they're about the best and most versatile of the lot imo.
Damo on 19 Apr 2012
In reply to UKC Articles:

260 is too heavy for a baselayer, unless you're standing around. Go thinner. It needs to be skin tight to work properly, regardless of how that looks. I say merino doesn't wick as well as synthetic and takes longer to dry. Smell is irrelevant for day or overnight use. Try a light polypro base with zip collar and a light pertex hooded windshell on top. Get used to being 'comfortably chilled' at the start so you don't overheat when moving.
captain paranoia - on 19 Apr 2012
In reply to colina:

> too cold to wear just a layer and overheating if im wearing a soft shell

As Guy says, that's the ideal time for a Pertex windshirt. I was going to say that in my first reply...

> soft shell is a good quality rab at around £100

But it could be insulated, it could have a membrane, or it could be a simple stretch woven. 'Soft shell' is a very vague description for a very wide range of products and technologies. So 'quality softhsell' is pretty meaningless in terms of receiving advice; we'd need to know exactly what type it is...

And, as Damo suggests, 260 weight merino is a little heavy IMHO. Merino does soak up moisture, and I think the lightest weight is best for base layers. It's more fragile, though; light, strong, cheap; pick any two...
In reply to Damo:
> Smell is irrelevant for day or overnight use.

You must be one of those annoyingly sweet smelling people like my wife who never get whiffy, 'cos my synth tops pongs in the armpits at least, after a 30 minute bike ride to work!
ads.ukclimbing.com
Damo on 21 Apr 2012
In reply to UKC Articles:

Good article here on recent developments regarding Gore's business practices and competition with other materials, including unbranded eVent, DryQ etc:
http://www.outsideonline.com/outdoor-gear/Insane-in-the-Membrane.html?page=all

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