Common folklore says that we lose most of our body heat through our head.
The truth is that the head is only about 10% of the body surface area. This means that the head would need to lose 40 times as much heat per square inch as any other part of the body.
Someone did an experiment with volunteers and wired them to monitor their core temperature. They were placed in cool water as they were monitored. As it turns out, we lose heat through any exposed part of our body and the amount of heat we lose depends on the size of the exposed area. You do not lose heat faster throught the scalp when compared to any other part of the body with the same surface area.
An interesting fact is that as you exercise, there is increased blood flow to the brain. This increases the percentage of heat lost through the head to about 50% of total body heat loss. But as the person exercises, the muscles require more oxygen which in turn increases blood flow. For the body to maintain normal core temperature, the skin vasodilates which increases blood flow to the skin to cool the blood. The final result is that there is a decrease in the total blood flow to the brain and a decrease in the percentage of toal body heat lost through the head to about 10%. Once a person starts sweating, the percent lost through the scalp drops back down to 7%.
With hypothermia, if the person is at rest, the heat loss through the head is about 7%. If the person begins shivering, the per cent of heat loss via the scalp can increase to 55% so it is important to portect the head of a hypothermic person.
In hypothermia, shivering is like exercising.