Interesting observations Paul. That article,( sent to Folkalist <img src="/forums/images/graemlins/wink.gif" alt="" /> ) sheds some light. You can go a few hours quite underdressed, because as you vasoconstrict your outer 1" of flesh slowly gives up heat, making up for the deficit, plus the skin itself starts to act as an insulator. Eventually however, you gotta put more clothes on or increase your activity level. People can acclimatize in being able to tolerate colder skin temperatures, thereby utilizing the outer 1" of flesh as insulation. He says however that bodyfat doesn't play a huge role in insulation value because it isn't distributed evenly enough like blubber on a walrus. I think it must help some though. It might not prevent frostbite, but it certainly adds some insulation in some places.

The practical heat storage of the body is about 100kcal, which while sitting in camp could allow you to lose 150kcal/hr for 2 hours while only generating 100kcal/hr. The insulation value of human skin can be 1 or 2 clo. Wool can also act to generate some heat by capturing the 20kcal per hour released to the wool as water vapour. This effectively increases its r-value by 20%, but the effect only lasts until it gains 35% of its weight in moisture, and then it needs to be effectively 'recharged' by losing moisture somehow, either by an increase in body heat, or solar insolation, or from a fire. It can absorb more than that, but the effect starts to become negated by an increase in thermal conductivity, rather like internal shorts in a battery. A dangerous corolary to all that is that by utilizing the temporary boost from cold climate acclimatization and falling skin temperatures and from wools vapour heat recovery you can get lulled into a false sense of security. Clothing tests really need to last 24 hours or more, not just 2-4 hours. Something to bear in mind. Another good rule is to maybe skimp on clothing, or on your sleeping bag, but never both.