Author Topic: A question about waterproof clothing  (Read 2156 times)

Steve922

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Re: A question about waterproof clothing
« Reply #15 on: 00:20:24, 24/01/18 »
Wow, its complicated, 'ain't it?  I've never been able to afford GopreTex before so never really looked into it. I just assumed it worked by magic.

sussamb

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Re: A question about waterproof clothing
« Reply #16 on: 06:34:15, 24/01/18 »
Just hold that thought and you'll be fine ...  ;D

Worth anyone reading this article though, it's been posted on this forum before https://andy-kirkpatrick.com/articles/view/the_truth_about_breathable_waterproofs
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jimbob

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Re: A question about waterproof clothing
« Reply #17 on: 13:40:29, 24/01/18 »
 O0 Sussamb , great article. Much food for thought.
 I tend to use a cheapy poncho and shorts in very heavy wet weather , whilst not quite an umbrella it comes a close second, in my humble point of view. (Well, at least it means I don't have to carry a waterproof knapsack cover, or something extra to sit on. ;D )
« Last Edit: 18:35:04, 24/01/18 by jimbob »
Too little, too late, too bad......

Sloth

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Re: A question about waterproof clothing
« Reply #18 on: 17:51:32, 24/01/18 »
Good article sussamb.  O0

Kukkudrill

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Re: A question about waterproof clothing
« Reply #19 on: 21:35:23, 24/01/18 »

lol. classic definition-of-a-word situation  ;D

however.....turns out a some of it isn't really true anyway. The real way Goretex works is more complex and nothing like those little pictures of vapor coming directly through the fabric.

https://www.scribd.com/doc/66945116/Introduction-to-Waterproof-Breathable-Membrane-Technology.

So it seems that the PTFE layer (under the face-fabric) is a web of fibres with gaps easily large enough for liquid water to pass through, but so hydrophobic that it doesn't. So that's the main method of keeping water out. Then under that is a PU layer which is continuous not filamentous - it does not have pores sized to let vapor out. Any pores it has are too small for that. But it has been made hydrophillic. Sweat, be that vapor or liquid, gets attracted into the PU layer and diffuses through it until it hits the PTFE layer which is dry because of it's hydrophobic nature, and there the water can evaporate. So it's not "breathing" at all really. If the PTFE layer gets compromised by dirt or detergent then it's no longer as hydrophobic and channels form that allow water to pass inwards to the PU layer. Once the top of the PU layer is as wet as the inside, there is no net diffusion outwards and so it cannot "breath" anymore and in fact could start to transfer water the other way but that would only happen if the PTFE layer is significantly compromised. The start of that compromise would be the breakdown of the DWR since that stops water even getting to the PTFE layer in the first place.

So fundamentally, Goretex fabrics are not breathing at all and do not let water just vapor pass though but instead are effectively wicking water to a dry surface. I never knew that.


Won't pretend that I can understand all the technicalities, but this doesn't sound right to me. It makes Gore-tex sound a bit like the Paramo Nikwax Analogy system in the sense that there is no actual physical barrier to liquid water, but Gore-tex and Paramo are different. As I understand it, if you're wearing Paramo trousers and you sit in a puddle you'll get a wet bum, whereas if you're wearing Gore-tex trousers you won't.


Besides, Gore-tex states very clearly that "The GORE-TEX® membrane has 9 billion pores per square inch, with each pore 20,000 times smaller than a water droplet. These tiny holes are too small for water and wind to pass through from the outside, which is how we can guarantee you'll stay dry and warm in a garment made with GORE-TEX® fabric. But these same pores are large enough for moisture vapor to pass through, so your body's perspiration is able to escape and you don't get clammy and uncomfortable. That's what 'waterproof/breathable' is all about." I got this from https://www.gore-tex.com/support/frequently-asked-questions. If the site you've quoted is correct, then Gore-tex is lying outright. Wouldn't Gore-tex be inviting serious trouble by doing so?
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Worcester John

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Re: A question about waterproof clothing
« Reply #20 on: 22:01:45, 24/01/18 »

It might be OK to sit in a puddle in Gortex over trousers for a few minutes but I know that if you sit on the seat of a mobility scooter for a few hours in the rain you will get a wet bum.


If the vapour has nowhere to go it has to stay on the inside of the garment. :(

Peter

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Re: A question about waterproof clothing
« Reply #21 on: 23:30:48, 24/01/18 »
If you only consider the official version of 'breathable' you would expect to see people walking and 'steaming' like a racehorse.
I've never seen anyone with their own vapour cloud.
So, is it really the case that 'breathable' works in theory but barely at all in practice?


Then again if we wore plastic coats it would be awful, so it must work??


Is it Buffalo that gets wet but keeps you warm or cool depending on whatever it depends on???


My brain hurts and I'm going to bed.  :-\
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NeilC

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Re: A question about waterproof clothing
« Reply #22 on: 08:34:47, 25/01/18 »

Won't pretend that I can understand all the technicalities, but this doesn't sound right to me. It makes Gore-tex sound a bit like the Paramo Nikwax Analogy system in the sense that there is no actual physical barrier to liquid water, but Gore-tex and Paramo are different. As I understand it, if you're wearing Paramo trousers and you sit in a puddle you'll get a wet bum, whereas if you're wearing Gore-tex trousers you won't.

Besides, Gore-tex states very clearly that "The GORE-TEX® membrane has 9 billion pores per square inch, with each pore 20,000 times smaller than a water droplet. These tiny holes are too small for water and wind to pass through from the outside, which is how we can guarantee you'll stay dry and warm in a garment made with GORE-TEX® fabric. But these same pores are large enough for moisture vapor to pass through, so your body's perspiration is able to escape and you don't get clammy and uncomfortable. That's what 'waterproof/breathable' is all about." I got this from https://www.gore-tex.com/support/frequently-asked-questions. If the site you've quoted is correct, then Gore-tex is lying outright. Wouldn't Gore-tex be inviting serious trouble by doing so?

I had the same thoughts about it being like Paramo but I think that's operating at a more macro level with regards to moving water.

I'm pretty sure that technical link is correct. It's not the only source for that info. A less technical but aligned explanation is in REI's site here.  And an even more technical explanation than the first one here

I would guess that Goretex aren't outright lying but rather using an explanation they think people will understand.  So what they've done is to focus on the PTFE layer only and been a bit casual/misleading about the language. Drops larger than the gaps would form on PTFE but that's because of the hydrophobic effect stopping the water passing rather than the other way around.


Goretex say nothing about the PU layer as a rule but there is no doubt there is one (it's one of their patents I believe) so I think that tells us something about how they've chosen to market it.

BTW, there are air bubble tests on Youtube: https://www.youtube.com/watch?v=6TmzwZgEVmA which show you can force air quite easily through eVent fabric but not through Goretex. If Goretex really just relied on holes that let vapour through then forced air would get through too. eVent doesn't have the PU layer and air can be pushed through.

I'm only going on what I'm reading but it would appear to be correct.
« Last Edit: 09:15:46, 25/01/18 by NeilC »

Kukkudrill

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Re: A question about waterproof clothing
« Reply #23 on: 20:47:31, 25/01/18 »
You've got me convinced  :)   The REI site is clearer than the Scribd article and also, I think, more balanced in how it presents the facts. The Scribd piece gives the impression that Gore-tex are telling an outright fib whereas the REI site suggests that they are telling part of the truth. Of course this is a difference in emphasis more than anything else. But the Scribd piece does contain a scientific howler: it says PTFE has high surface energy whereas the complete opposite is true, as explained by the REI page.


It might be OK to sit in a puddle in Gortex over trousers for a few minutes but I know that if you sit on the seat of a mobility scooter for a few hours in the rain you will get a wet bum.

If the vapour has nowhere to go it has to stay on the inside of the garment. :(


You've got me thinking. Not only will moisture inside the garment remain trapped, but (maybe) your bum will warm up the moisture on the seat and make it evaporate, and then there will be nothing to stop it passing through the Gore-tex and collecting inside ... which indeed results in a wet bum.
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NeilC

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Re: A question about waterproof clothing
« Reply #24 on: 09:03:33, 26/01/18 »
the Scribd piece does contain a scientific howler: it says PTFE has high surface energy whereas the complete opposite is true, as explained by the REI page.


Hey good catch, I'd not noticed that and you're right.

(maybe) your bum will warm up the moisture on the seat and make it evaporate, and then there will be nothing to stop it passing through the Gore-tex and collecting inside ... which indeed results in a wet bum.


That's what Andrew Skurka goes on about in his blogs - when the humidity is the same on both sides then no net transfer happens, and if outside is more humid, then it goes inwards, which would explain it. This might be particularly likely in boots where the goretex liner is up against layers of sopping wet leather which is warmed by the foot. That's surely at 100% humidity or close?

ninthace

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Re: A question about waterproof clothing
« Reply #25 on: 14:20:47, 26/01/18 »

That's what Andrew Skurka goes on about in his blogs - when the humidity is the same on both sides then no net transfer happens, and if outside is more humid, then it goes inwards, which would explain it. This might be particularly likely in boots where the goretex liner is up against layers of sopping wet leather which is warmed by the foot. That's surely at 100% humidity or close?
Not sure that is entirely true if temperatures are different on either side of the membrane? Warm air can carry more moisture as vapour than cold air.
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NeilC

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Re: A question about waterproof clothing
« Reply #26 on: 23:19:26, 27/01/18 »
Not sure that is entirely true if temperatures are different on either side of the membrane? Warm air can carry more moisture as vapour than cold air.


I'm sure temperatures will make a difference.
« Last Edit: 23:39:32, 27/01/18 by NeilC »

ninthace

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Re: A question about waterproof clothing
« Reply #27 on: 13:37:39, 28/01/18 »

I'm sure temperatures will make a difference.


Today I was out on the SWCP wearing a lightweight jacket which has a water resistant outer layer over a membrane with a mesh liner over thin fleece. When I set off I started to get a bit warm so I opened the jacket and undid the cuffs. About 45 mins later the cuffs were dripping and the backs of my shoulders were wet with condensation forming on the membrane.  I zipped the jacket back up and tightened the cuffs and within a few minutes the condensation had disappeared and I felt a lot more comfortable.  I presume this was because the increase in temperature inside the jacket made the membrane more efficient even though the humidity inside the jacket was presumably higher than outside as it wasn't raining (for once)
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