How do humidity and air movement affect the performance of breathable jackets?

Question

In what ways do humidity values or air motion affect the performance of breathable waterproof jackets?

Answer 1

Humidity and air circulation disturb the normal function of moisture-wicking jackets. When there is low humidity, the air has the ability to compress water vapor molecules thus making the jacket breathable. However, in tropical regions, for instance, rain forests, sweat can hardly escape from the jacket because the surrounding temperature is too humid for evaporation to occur at a high rate. Most importantly, if there is no airflow, there is nothing to evaporate off the skin. However, jackets are supposed to provide partial wind penetration because that is what they’re designed for. Components of jackets such as pit zips can create ventilation; however, one must question the need for a breathable jacket if the user must use ventilators.

Comments

What you miss in this content is that, as long as the temperature inside the jacket is higher/warmer than outside the jacket, there is still a vapor pressure differential that should drive vapor from inside the jacket to outside the jacket, even when the outside is wetted out. The problem is that this differential is generally not sufficient to transfer the amount of sweat generated while hiking.

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Well, it is not always raining, is it? Sometimes it is cold and then I sweat. And if I wear Gore-Tex that sweat is actually ventilated out, while the jacket is keeping me warm.

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So this is a surprise to anyone? I've used them since the 70s, and they never worked perfect, but they were noticeably better than the hard-coated urethane jackets we used before. When you're backpacking, you only want one wind/rain shell. Sitting around in a rubber jacket to  keep the wind off sucked, so the so-called waterproof breathable jackets were way better for that application. A few of my friends had expensive ventile parkas which might have been the best compromise, but like today, they were very expensive.

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I wear a goretex jacket and pants for resort skiing. They have been 100% waterproof even during all day wet snow, with falling, sitting on the snow etc, until the seams go or they delaminate.  For resort skiing, in a gondola/bubble or a mountain restaurant, you can see the steam coming out through the jacket, and you don't have to keep farting around with the front zip, pit zips or taking the jacket off.  Similarly if it stops snowing, the moisture underneath comes out. So waterproof AND breathable is useful if it sometimes stops raining or snowing on you. I get that this is a hiking channel, but think it's worth a mention that the situation is different for skiing. ps all that stuff about needing a humidity gradient between inside and outside applies also if you're wearing just a pair of shorts or a wicking baselayer. Sweat will not evaporate when the humidity is high.

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Great content. I don't like Gore-Tex in heavy rain, but it works great for most of what I do, which is winter downhill skiing. It keeps me dry and warm because even when it is snowing the outside humidity is pretty low out here in the west. I have a buddy that bought a cheap waterproof (not breathable) jacket for skiing - bragging that it only cost about $90. Every day after skiing, he would take off the jacket and was pretty much soaked with sweat, while I was almost completely dry. Moisture was dripping off the inside of his waterproof jacket. For cold, dry conditions, fabrics like Gore-Tex are hard to beat. If I was working as a lift operator, I would definitely wear a big loose waterproof (not breathable) jacket - for that the expensive fabric would make no sense.