I have known for years that Goretex doesn't breathe when it is high humidity (or raining) .. noted because of how damp I would always become inside, as my sweat vapour turned back to water .. so I left such jackets and moved to cape style ponchos, free flowing air underneath so no sweating and totally waterproof too -
Goretex can only 'breathe' in low humidity dry weather and cannot work when the outer surface is wet - and now - Hurrah!! here is the proof! (Save a substantial amount of money!). ...
@David, this is an amazing piece of work of someone clearly trying to put as much objectivity into something that is just full of what, at worst, would be considered tabloid journalism. I don't see any scam here by the outdoor clothing companies. They have known for many years about the limitations of Goretex as a particular fabric, as has the manufacturer. Many have worked on creating alternatives that improve on one or more aspects of the performance required for good raingear, and developed new fabrics that do that. I have seen and used raingear with trade names like eVent, Hydronaute PRO, ngx3, c_change and VaporTEC, and there are bound to be many more.
You claim to have known about the limitations of Goretex 'for years'. Haven't we all? When I saw this, amongst my first thoughts was 'this is hardly news, we first discussed this years ago', and then went to see if I had made any personal contributions on this, and found this from 2015, not quite a decade ago:
At a technical level, permeable membranes like Goretex transpire water vapour, and that requires a difference in vapour pressure. I don't think they are naturally one directional, but because body heat raises the vapour pressure inside an article of Goretex equipment, the flow is away from the body. If you sweat so much that your body heat is insufficient to turn all your sweat to vapour, that moisture won't be transpired, and then you get the build up of sweat on the inside. It is not the fabric leaking - it is in fact working to stop the passage of moisture, just that it is the moisture (not vapour) on the inside not being let out.
In the same way that loss of the DWR layer on the outer surface will allow moisture to sit on the surface, and reduce the breathability of the fabric, I suspect accumulation of moisture on the inside will have a similar effect.
I recall others who have made similar contributions about this matter that have provided similar or even better explanations than my simple explanation back then. This is important because you seem to have a presented a poor description of both the physiology of sweating, and the physics behind the operation of a permeable membrane and DWR treatments to justify your advocacy for ponchos. Let me make some short observations on both.
Sweat does not form as a vapour, but as liquid. When your skin is dry, that is not an indication you aren't sweating, but that the sweat is able to evaporate very quickly as it reaches the surface of the skin. The energy required for this is the build up of heat in the body, and removing that heat by evaporating sweat starts to cool the body and regulate the heat build up. But as we continue to work or walk, as daytime temperatures increase or as humidity increases, we either produce more sweat in an attempt to keep our bodies cool, or in the case of humidity increases, less sweat can be evaporated from the skin. Having no liquid sweat forming on the skin is not an indication you are not sweating, but that you are exerting a level of effort that your body's natural heat regulation mechanisms can control in the conditions that exist at the time. Alternatively, you have gone into heat stress, and really bad things are now about to happen if you don't stop, rest and get help.
For water vapour to cross any permeable membrane, like the waterproof layer of Goretex, all that is required is a difference in vapour pressure between one side of the membrane and the other. The greater the difference, the more vapour will cross the membrane. And when there is only a small difference in vapour pressure, then very little vapour will be able to cross the membrane. Which leads to the phenomena that when it is raining, and one continues to work or walk, the amount of vapour being transpired is not sufficient to keep our skin dry, the sweat we form doesn't evaporate because we have saturated the small amount of air inside the rain gear, and then sweat wets any clothing we are wearing underneath our raingear.
Goretex not 'breathing' when the outer layer has 'wet out' was the other issue you raise, and it is true that when the surface layer of any of these waterproof garments gets dirty or the DWR treatment has been compromised, water can soak into and spread across the outer layer of the fabric. This 'wetting out' is generally obvious, and is quite different to the surface just being wet when it is raining. While the water proofing of the rain gear isn't compromised by this, the breathability will be. Why it is an issue is not clear to me. Proper care of the jacket will, in my experience, take care of this. Most of the jackets I have worn over the years have care instructions that haven't been too difficult to follow, and with an occasional treatment with a spray on or soak in DWR, the effectiveness of the material can be restored.
I don't think your arguments, or the video you have linked to, actually create a compelling case against Goretex or any of the more modern vapour permeable membrane based fabrics as rain gear. Certainly, it is good to see that the person who make the video has realised something that I thought had been well known for some time, and has used some very informative material in presenting his concerns. But there is far to much hyperbole about this being a scam for me to be convinced by those elements of his discussion.
