Does gortex act as a vapor barrier…

NO!

Here is a diagram of GORE-TEX (and similar WPBs) in action.

Here is a diagram of a vapor barrier in action.

YES….or sorta.

It is not as good a vapor barrier as others, but it should be treated like a vapor barrier when layering under a quilt.

There are better vapor barriers, but use it like one if that is all you have.

I'm inclined to think it does. Here's why.

My understanding is that the inner surface of wp/b materials absorb moisture before passing it through to the outside. If it's really cold I think it freezes in the material because I sometimes get a layer of frost on the inside of the jacket. I don't think ice is too breathable.

Theoratically it goes like this.

Vapour can permeate through a fabric if there is a vapour humidity differential between each side of the fabric. Basically the drier it is on one side on the more humid it is on the other the more vapour will permeate through the fabric.

Warm air can hold a lot of vapour, cold air can't hold that much vapour and is (as you may have experienced) very dry. You might be inclined to think now that in winter the climate on the inside of your jacket is warm and high in humidity and on the outside there is very very little humidity so you think you'd almost be vaccuum dried inside your jacket, but it doesn't work like that. When it is very cold, the dewpoint (the point where water vapour turns into moisture) can be on the insid of your jacket and what happens is, as you experienced, that liquid water freezes on the inside of your jacket.

So what happens inside your jacket on a cold winter day is that before your GoreTex can do anything (absorb, breathe) with your excreded water vapour it has already turned into liquid water or ice and those (luckily) can't permeate through GTX fabric.

So nope, GTX isn't a vapour barrier, however if you'd make a breathability scale from being butt naked (veeery breathable) to wearing rubber (not breathable at all) GTX is more on the rubber side, though GTX would disagree.

Eins

Adding to Einstein X's comments,

if you have sufficient ventilation say at the neck of a sleeping bag, the greatly hindered breathability of Gore in cold conditions will likely force alot of moist air out through this vent.

As a very short term measure (over time you will no doubt have some freeze build up), I think Gore could work as a vapour barrier, but the question is, why bother? If you are into wearing vapour clothing rather than say a liner in a sleeping bag, and multi-use, then I doubt that wearing your jacket and pants from the day will be a good idea inside a sleeping bag. Any latent moisture on the outside of your Gore will pose a risk (lets be honest, no DWR is perfect).

A proper lightweight vapour barrier made of say cuben fibre would way sweet stuff all. I say forget Gore.

You could always try out a PVC rain suit for $5 and just ventilate that.

Thanks for all your comments so far. The amount of knowledge in these forums is impressive.

Another reason I brought this up is the discussion in some of the other threads about Mark Twight's book extreme alpinism.

If I remember correctly (could most definitely be wrong here), in the clothing section he recommends that the more breathable a layer is, the further it should be away from you skin. Reason being that it is easier to drive moisture out of you system by body heat.

Now, My least breathable layer would be my waterproof layer, which combined over a base is comfortable enough while on the move in the cold. For stops and what not a belay type jacket would be thrown on.

Now of course the waterproof isn't going to block all internal moisture from escaping, but it should slow it enough to let your body heat drive out what little that does pass through. Also, by letting some moisture out it would seem to somewhat reduce clamminess that can be associated with VB layers.

I realize this idea is out there and that some first hand testing is necessary, but appreciate opinions and experience of others here on this idea.

Also I should note that I do have quite a bit of experience in using VB socks and owe my ten toes to the concept.

Do you refer to the part where he explains the layering on top approach instead of the classic layering underneath approach (p83)?

It's all kind of logic. Assume you wear a baselayer and a waterproof shell. The baselayer doesn't act as a real thermal barrier so the warmth produced by your body is quickly transferred through the baselayer to the next layer. This means that the inside of your waterproof jacket is kept relatively warm and efficient. Because moisture can be driven out, you prevent moisture build up inside your layering system and since moisture/moist air conducts warmth 24 times faster than dry air, you will remain more comfortable.

If you would put on an insulating layer underneath your shell jacket, less warmth would be transferred to your shell jacket (your insulating layer would isolate your shell from your warmth producing body), your shell layer would cool much faster. A cool shell layer is less efficient in transfering moisture, keeping the moisture inside and chilling your interior layers and yourself.

If you put your insulating jacket on top of your shell jacket, your shell layer (being the greatest barrier to vapour transfer) is kept warm and efficient, making it easier to transfer moisture to the next layer = insulating layer which should be much more breathable than your shell layer and thus showing little resistance to moisture transfer to the outside.

Personally, I think that a VB is usefull in non-active situations where your body only produces insensible perspiration (to keep your skin moist). In active situations, where your body uses sensible perspiration to get rid of excess warmth produced by your body, I'm not convinced that VB clothing is usefull.

Do you refer to the part where he explains the layering on top approach instead of the classic layering underneath approach (p83)?

It's all kind of logic. Assume you wear a baselayer and a waterproof shell. The baselayer doesn't act as a real thermal barrier so the warmth produced by your body is quickly transferred through the baselayer to the next layer. This means that the inside of your waterproof jacket is kept relatively warm and efficient. Because moisture can be driven out, you prevent moisture build up inside your layering system and since moisture/moist air conducts warmth 24 times faster than dry air, you will remain more comfortable.

If you would put on an insulating layer underneath your shell jacket, less warmth would be transferred to your shell jacket (your insulating layer would isolate your shell from your warmth producing body), your shell layer would cool much faster. A cool shell layer is less efficient in transfering moisture, keeping the moisture inside and chilling your interior layers and yourself.

If you put your insulating jacket on top of your shell jacket, your shell layer (being the greatest barrier to vapour transfer) is kept warm and efficient, making it easier to transfer moisture to the next layer = insulating layer which should be much more breathable than your shell layer and thus showing little resistance to moisture transfer to the outside.

Personally, I think that a VB is usefull in non-active situations where your body only produces insensible perspiration (to keep your skin moist). In active situations, where your body uses sensible perspiration to get rid of excess warmth produced by your body, I'm not convinced that VB clothing is usefull.

Do you refer to the part where he explains the layering on top approach instead of the classic layering underneath approach (p83)?

It's all kind of logic. Assume you wear a baselayer and a waterproof shell. The baselayer doesn't act as a real thermal barrier so the warmth produced by your body is quickly transferred through the baselayer to the next layer. This means that the inside of your waterproof jacket is kept relatively warm and efficient. Because moisture can be driven out, you prevent moisture build up inside your layering system and since moisture/moist air conducts warmth 24 times faster than dry air, you will remain more comfortable.

If you would put on an insulating layer underneath your shell jacket, less warmth would be transferred to your shell jacket (your insulating layer would isolate your shell from your warmth producing body), your shell layer would cool much faster. A cool shell layer is less efficient in transfering moisture, keeping the moisture inside and chilling your interior layers and yourself.

If you put your insulating jacket on top of your shell jacket, your shell layer (being the greatest barrier to vapour transfer) is kept warm and efficient, making it easier to transfer moisture to the next layer = insulating layer which should be much more breathable than your shell layer and thus showing little resistance to moisture transfer to the outside.

Personally, I think that a VB is usefull in non-active situations where your body only produces insensible perspiration (to keep your skin moist). In active situations, where your body uses sensible perspiration to get rid of excess warmth produced by your body, I'm not convinced that VB clothing is usefull.

I'm quite intregued in this concept, but I think you're forgetting one important factor which contributes to your shell being able to move vapour through the fabric.

There are three major parameter contributing to WVT: firstly there is the temperature of permeate. Ie cool water goes through a fabric more slowly than warm water (and ice cubicles don't go through GTX at all :D). The second parameter is the thickness of the fabric. Ie it takes more time to permeate through a thick fabric than it does to permeate through a thin fabric. But the last and equilly important factor is the windspeed over the fabric. If there is no flow of air over the fabric what so ever the relative humidity on that side of the fabric will get higher and higher and eventually there won't be a differential of relative humidity over the fabric anymore and there will also be no more vapour permeating the fabric.

So eventhough I think it's an interesting idea of keeping your WP/B layer close to the skin to keep it warm and so help it push out the vapour, I think you will loose most of the gained breathability by blocking the flow of air over the fabric by wearing an insulating layer over it.

Eins

Roy: At the start of this thread you mention a single base layer but what is that? At twenty below you should not have to do much ventilating as long as you don't have too much of a base layer on ( it's OK to ventilate if you have too much on underneath and would rather not change out). I'll have to look at my Twight book but the whole point of the WP/B layer next or close to the skin is that is the only place it can be when you are superactive unless you are going to sweat to death AND overheat. Twight is talking about wearing or trying to wear the 'perfect' amount of layers under the WP/B layer. BUT, for anyone that has used WP/B layers like this, it is understood that it is a Vapor barrier to some degree – at least to slow down air flow and convection at the same time it is a barrier to external moisture while ice climbing etc. When dressed to the absolute minimum under the WP/B layer, you need to keep the Layer sealed off because you are producing just enough heat to stay warm. WP/B will contribute to sweating especially when too much insulation is under it, so what you do is eliminate the insultion. Most beginners way overdress under WP/B layers and then sweat to death. To make it all work properly you have to stradle the line of being cold once you stop at all, or cold when you start off (something beginners hate – but experienced people hate being too hot and know how to get to not being too hot) hence the belay jacket going on right away when the climbing stops. Climbers of Twights caliber are human furnaces and overheat very easily, so what Twight does, and the degree that he may do it, could baffle a beginner ( punn intended ).

My use of the term vapor barrier could cause a problem here. I did not mean it in the sense of VBs that are meant to keep skin moist at cold temps but simply as a barrier that is much more of a barrier than say an open base layer. Whenever you stop air permeability you are holding heat and moisture. Because WP/B fabrics hold both you must learn to not overdress so that the cooling aspect of sweat does not kick in. It is possible to overdress underneath any tight weave shell. It is possible to overdress without a shell at all. Shells of any kind do make it possible to carry or wear fewer layers.

Twight may cause confusion when he pulls the insulating parka over the WP/B layer but it is not different than putting it on over a just a fleece top. Twight is just making the point that is is a waist of time and energy for a speed climber to take a the WP/B layer off before putting on a belay jacket.

> If you put your insulating jacket on top of your shell jacket, your shell layer (being the greatest barrier to vapour transfer) is kept warm and efficient, making it easier to transfer moisture to the next layer = insulating layer which should be much more breathable than your shell layer and thus showing little resistance to moisture transfer to the outside.

Unfortunately, this logic contains one fatal flaw. And 'fatal' could be the literal result in some cases.

Yes, the WP/B layer may stay warm and dry, and transmit your body moisture to the next outer insulating layer – at the start. I have to ask what purpose the WP/B layer is now serving – none at all as far as I can see.

However, assuming the outside world is seriously cold, then the freezing point must be somewhere inside the insulating layer, between your warm WP/B layer and the outside world. This is where you will get a build-up of ice: INSIDE your insulating layer. Make no mistake: ice will form there. The WP/B layer has done NOTHING to stop this.

It gets worse. As your body temp and heat output fluctuate, so the position of the ice-forming layer will vary back and forth, eventually resulting in a thick frozen layer inside your 'insulating' layer. Needless to say, the insulating properties will die, and you will be left freezing to death.

If you are going to wear a VBL, you must make sure it really does block ALL the vapour, so that you don't get a build-up of ice in the layers outside it. And remember: WP/Breathable is NOT a Vapour Barrier Layer. One breathes; the other does not. Ideally, while wearing a VBL you should ideally make sure that you are cool, not warm and sweating.

Basically, a VBL layer inside a sleeping bag is fine, but a VBL while you are actively walking is tricky. If Mark Twight wants to wear one while doing 'extreme alpinism', good luck to him. But he probably spends a lot of time standing still, belaying, and this is very different from active walking with a pack.

(Exception: VBL socks are in a class of their own. They can actually serve a slightly different function, depending on the outside temperature.)

So what use is a WP/B layer when walking in sub-zero conditions? Well, as an outer shell it blocks the wind … and this is useful of course.

One useful technique, IF you can manage it, is to try to have the ice build-up on the inside surface of a thin shell layer, so that you can take it off and 'brush' the ice layer off it. In other words, try to control where the ice is going to form, in a place from where it can be removed. Not easy though.

Cheers

>>"Yes, the WP/B layer may stay warm and dry, and transmit your body moisture to the next outer insulating layer – at the start. I have to ask what purpose the WP/B layer is now serving – none at all as far as I can see.

However, assuming the outside world is seriously cold, then the freezing point must be somewhere inside the insulating layer, between your warm WP/B layer and the outside world. This is where you will get a build-up of ice: INSIDE your insulating layer. Make no mistake: ice will form there. The WP/B layer has done NOTHING to stop this.

It gets worse. As your body temp and heat output fluctuate, so the position of the ice-forming layer will vary back and forth, eventually resulting in a thick frozen layer inside your 'insulating' layer. Needless to say, the insulating properties will die, and you will be left freezing to death."<<

In my experience this doesn't happen. Maybe if you are hiking with the insulating layer over the WP/B and sweating, but I think the idea is to have a light action suit that you hike/move in and then when you come to a rest, you put the insulating layer over the WP/B. This maintains the temperature differential between the inside micro climate and the outside environment, driving any (and it should be minimal) residual moisture through the WP/B and also thorough the more breathable insulating layer. When you start hiking again, you shed the insulation and get going.

Another non VB technique that works well is to wear a light wicking layer and a very light (Golite ether/wisp, Patagonia Houdini or Wildthings UL windshirt) breathable layer just over it. Then a soft shell or other breathable insulation just over that. This creates a micro climate close to the body that I have found to increase warmth
significantly while avoiding the clammy feeling of a VB and the potential for 'flash freeze'. Wind usually won't carry away that warm air, even when it gets through your softshell layer.

I think so much of temperature regulation is what works for the individual.

I agree that WP/B are not super effective in sub-zero conditions because they are not nearly as breathable as we are led to believe. Roger makes an excellent point that WP/B's are not effective vapor barriers.

Eins, Roger,
I actually agree with most of what you said. Still, perhaps a few things to clariy my thoughts.

"So eventhough I think it's an interesting idea of keeping your WP/B layer close to the skin to keep it warm and so help it push out the vapour, I think you will loose most of the gained breathability by blocking the flow of air over the fabric by wearing an insulating layer over it."

Well, I never said it's a perfect system. But my experience is that it works better than the classic layering system. The question is also: do I loose most of the gains or do I loose all the gains? And just to be clear: I never use the insulating layer while being active. I produce more than enough heat myself and wearing the insulating layer causes me to overheat, activating the body mechanisms for cooling of and that's tha last thing I want.

" Yes, the WP/B layer may stay warm and dry, and transmit your body moisture to the next outer insulating layer – at the start. I have to ask what purpose the WP/B layer is now serving – none at all as far as I can see."

Kind of agree. While taking a pause, I try to find some cover. Perhaps the WP/B layer isn't serving its primary purpose at that point (keeping rain outside) but it just has become part of the system now to keep me warm.

" However, assuming the outside world is seriously cold, then the freezing point must be somewhere inside the insulating layer, between your warm WP/B layer and the outside world. This is where you will get a build-up of ice: INSIDE your insulating layer. Make no mistake: ice will form there. The WP/B layer has done NOTHING to stop this. It gets worse. As your body temp and heat output fluctuate, so the position of the ice-forming layer will vary back and forth, eventually resulting in a thick frozen layer inside your 'insulating' layer. Needless to say, the insulating properties will die, and you will be left freezing to death."

Again I sort of agree. Again the question is: will the classic layering system perform better? Personally I don't think it will. BTW, in serious cold weather, I don't see a reason to carry a waterproof shell anyway. The best strategy under such conditions is to sweat as little as possible by lowering the activity level or wearing less clothing with a high degree of breathability (just as explained by Mr McHale).

Although Mark Twight's ideas are particularly focussed on the alternation of climbing and belaying, I feel they are as usefull for the combination of 1)walking and 2) resting or making camp. Of course, it is as important to be able to adapt to changing situations and not see the "Mark Twight approach" as something which should be followed no mather what happens.

As I said before, I'm not convinced that using VBL in active situations is usefull, with the possible exception for socks and gloves (where I guess this as something to do with the position of hands and feet as extremeties positioned far away from the interior heat source, combined with the great surface area of both).

Gore-Tex ia a vapor PERMEABLE material, not a vapor barrier. But it aint nearly as "permeable" as we'd like. Do I would only use waterproof material for a VBL garment.

As a former Nordic National Ski Patroller my experience with Gore-Tex on cold, windy, 10 F days is that, like my regular rust color poly cotton patrol jacket, it would accumulate frost on the GTX membrane, particularly on my back & my arms.

GTX isn't breathable enough to handle all the vapor given off while speeding along a track carrying a 15 lb. patrol fanny pack. Maybe eVent is enough more breathable it wouldn't be plagued (as much) by this frosting problem, but I've never had the $$$ to invest in an eVent parka to find out if it's THAT much better.

Howsomever, I could remove my GTX parka in the field & just shake the frost off & down to the hem/cuff areas where the 65/35 poly cotton official patrol jacket still held most of the frost in the weave after a good shake. Any GTX or eVent jacket with a mesh liner, at least at the hem area, would allow most of the frost to be shaken out – a design feature to look for in your next purchase.

So, yes, the GTX parks had that advantage, plus being more windproof. And that's the shell I turned to when the weather got bitter.

Eric

Apologies for the delayed response, haven’t had a moment to sit down and write a good response until now.

Tom, I’m not sure if that’s the page or not but it sounds right. I don’t have the book anymore (borrowed it from a friend, like a year ago). I’m with ya it does seem somewhat logical. I guess the big question is if body heat is enough to drive out the moisture that does pass through the WP/B through all of layers.

Eins, you’re right I hadn’t thought of that. Do you think body heat would have any affect to reduce the humidity on the outside of the shell?

Dan, my base layer is usually just a long sleeve capilene 2. Even with that and just the shell I can work up a sweat if I exert myself too hard, so I try to keep it steady and shoot for “comfortably cool” while on the move. Good point about it being no different than a fleece. I guess I just over analyzed what he was trying to say.

Roger, that’s exactly the situation I would be trying to avoid. I was hoping not to take a dedicated VB layer to reduce a little bit weight. Sounds like I better look elsewhere.

Ryan, thanks for the tip. I will try it out and see how it goes.

Eric, I agree some of your experiences match mine from when I was in the Marines.

Thanks for all the input everyone, you’ve all been extremely helpful!

>>Do you think body heat would have any affect to reduce the humidity on the outside of the shell?<<

The only thing body heat can do on the outside of your shell is make the air a bit warmer. This will result this warmer air being able to contain a little bit more moisture, but still this moisture won't be going anywhere due to the lack of wind. Eventually the humidity will become high enough so that there wont be a differential anymore and so no WVT. So basically the only benefit you'll have from the body heat is the WVT will stop a bit later.

Eins

Eins,
an interesting point but still a few considerations.
Even if the RH on the outside is 100% there can still be a vapourpressure gradient if the temperature gradient is high enough. I believe under normal conditions average skintemperature is 32°C and average RH is 65%. Assume your wear only a baselayer, then a shelljacket and then your insulation, what then would be the temperature on the outside of the shell jacket underneath the insulation. If the temparture isn't higher than 25°C, then there's still a small vapourpressure gradient and that's all that is needed.

Then your point about convection. I think also natural convection and other examples of forced convection have to be taken into account. If you can make the air on the outside of your shell a bit warmer, not only will it be able to contain more moisture but it will also be less dense than the surrounding air. Warm air rises and will be replaced by air which can be warmed again. Next to that, when your active, your body moves which makes the surrounding air and air inside your layers flow around. I don't know how big the effect is of both but I wouldn't say wind is the only factor.

> As a former Nordic National Ski Patroller my experience with Gore-Tex on cold, windy, 10 F days is that, like my regular rust color poly cotton patrol jacket, it would accumulate frost on the GTX membrane, particularly on my back & my arms.

Sounds as though this could also work with an eVent, EPIC or even silnylon shell in really cold weather. The silnylon would really lose most of the ice build-up, but maybe it would also accumulate lots more than the others. A bit risky maybe?

Personally I prefer an EPIC shell as it breathes moderately well. That's what I use in the snow as a shell now, and it works nicely over a light fleece, active or stationary. The fleece tolerates pack straps much better than any sort of padded jacket of course.

Cheers

>>Even if the RH on the outside is 100% there can still be a vapourpressure gradient if the temperature gradient is high enough.<<

Woubier, this might be true. There will always be a gradient due to the temperature difference, but if on the outside of your jacket RH is 100% this means that the air is already holding ALL the moisture i can. Eventhough you're trying to push out some moisture the air it's being driven to can't contain 101 or 102% humidity: it is already saturated so no moisture will be absorbed into that air and so NO WVT.

But I will give you the fact that there will still be some convection between your shell and the fleece due to the points you mentioned. And as I said before I think it's a very interesting idea to wear your shell closer to your body on cold days, but then I'm wondering when it really cold do you actually need a hardshell?

But enough theorising, can someone please put it to the test?

Eins

Eins,
not that I want to go on but …

"it is already saturated so no moisture will be absorbed into that air and so NO WVT"
actually, I would just exspect that condensation would take place.

"air can't contain 101 or 102% (relative) humidity"
well, just to tease you, theoretically speaking that's not correct. The extra amount of moisture would condens but to condense it needs condensation nuclei and when condensation nuclei are hydrophobic in nature condensation will take place at RH over 100%. However in practice this is rarely the case ;-)

"but then I'm wondering when it's really cold do you actually need a hardshell?"
Of course not. But I think the principle applies no mather what temperature.

>>actually, I would just exspect that condensation would take place.<<

Good point. But won't that take us back to the start? Water vapour now turns into liquid water and can now freeze somewhere in your isolation layer which you are wearing on the outside. So your choice now is ice build up inside your fleece or on the inside of your hardshell. As pointed out above, I'd choose the latter.

So what do we agree upon?

1/ wearing your shell close to your body will at least help drive the moisture to the outside of your shell.

2/ the isolation layer blocks (some of the) wind so the water vapour wont be transported away very efficiently.

3/ natural convection due to movement and heat rising will help transport some of the excess water vapour.

4/ build up of ice can happen inside your shell or inside your isolation depending on which one you wear on the outside.

Agree or disagree?

Eins