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Posted by Bill S on December 29, 2007 at 8:13:37 pm EST
In reply to Rain Gear posted by Scott S on December 29, 2007 at 10:54:36 am EST

Scott, Pre-Cip in my experience is very non-breathable. I have gotten wetter with it than any supposedly rainproof system I have tried before or since.

The principle behind waterproof/breathable fabrics will readily explain why it doesn't work in the conditions you encountered during the monsoon, and why a simple poncho works reasonably well. The basic physics of goretex, eVent, and the variations and imitations is the difference in vapor pressure between the two sides of the fabric, with the provision that the pores are open. They work well when the temperature is fairly low, and when the humidity outside is fairly low (such as during desert and high altitude rains, and high altitude snow storms where the water is all frozen as snow flakes). During the Indian monsoon (and some of the rains I was in during my trip the past couple of weeks in Tanzania, trekking through rainforest), the humidity was in the 80-90% range. WP/B fabrics don't work well if the gradient is that low (that is, humidity and hence vapor pressure from inside to outside the jackets is nearly the same). Your Frogg Toggs work on the same principle, except using layered polypropylene instead of the Teflon that Goretex uses - microporous so liquid water can't get through, but water vapor can. Big problem is first, the question of water vapor pressure gradient, but in addition, when the outside gets a film of water (thanks to body oils or just plain old dirt), the pores get blocked, so no breathability. Your sweat can't get out, so you get wet inside - especially in warm to hot conditions like India (or for me in Tanzania).

Ponchos (and umbrellas) allow a fair amount of air circulation, hence cooling. So in a rainstorm of monsoon scale, you can stay drier with a poncho or umbrella (of proper size and shape). The big problem with ponchos and umbrellas is that they tend to blow around. When the poncho tails blow up, the rain gets in. Side snaps that allow for a lot of ventilation partially solve that problem. I really wished that I had brought my old yellow, completely waterproof/nonbreathable poncho with me, and had worn it over my pack as Patrick, my guide, did. I would not have gotten as sweaty, hence wet.

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• Re: Rain Gear - calamity 18:39:01 12/30/2007

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