Just picked up a book called "the 2oz. Backpacker". Neat little book that contains quite a few suggestions regarding backpacking... The author spends a few pages talking about vapor barriers.
The section suggests that in cold conditions we should consider putting vapor-proof materials in direct connection to the body and put insulating layers outside of that. He states that it will reduce sweating (by keeping the area around the skin near a "naturally" humid state)--unlike putting it over the insulation, which will trap sweat that has been absorbed by the other layers. He claims that you will be warmer too--and won't need such bulky insulation layers.
Further, he writes that putting plastic bags or saran wrap around your feet before your socks AND surgical/plastic gloves underneath your regular gloves or mittens will accomplish the same feat. Warmth without added weight. And slightly damp/humid vs. dripping. Again, he stresses that the vapor barrier heat gain is proportional to the temperature outside (the colder the better).
This sounds fascinating and since his discussion was in-line with that recent Backpacker article on so-called "Breathable" fabrics and their lack of actual usefulness. Ideas? Have any of you used vapor barriers next to the skin (he suggested rain gear, wind shirts or trash bags with holes cut out)?