Many have found that wrapping their heads with aluminum foil not only acts as a vapor barrier, but it also protects them from the effects of evil secret government agencies. <img src="/images/graemlins/grin.gif" alt="" />

I have a fleece jacket from Cabelas that has a "windshear" layer sandwiched between two layers of fleece. Even though it is supposed to breath well, I found that it was too hot for moderate temperatures (50-60F) and would make me sweat too much. Now that it is colder out I find it does a great job at 30-40F.

I've always assumed that the idea is that under survival conditions one would cover themselves with the vapor barrier enduring any uncomfortable persperation, and wait for help to arrive. They shouldn't remove the barrier until alternative insulation or methods of warming are available - most likely after rescue.

I've been reading a lot about the supposed vapor-permiable materials and have come to the conclusion that they only work when someone is nearly comatose (not at all active). Any activity at all will result in excessive sweat accumulation. Right now I think the best bet for rain protection is a waterproof layer (plastic, coated nylon, ...) combined with very effective venting. Eureka's single-wall tents use coated nylon with lots of venting. Gore-Tex coats come with tons of venting holes & zippers. I tend to think waterproof boots rely on foot movement to pump out humid air. Someday I might try to design a poncho that has some kind of belt to limit the wafting from wind.