Up to 40-45% Half of your body heat is lost through the head, so also 50%
This idea was then perpetuated by a 1970s edition of a US Army survival field guide that recommended covering one’s head in frigid temperatures because “40 to 45 percent of body heat” is lost through the head.
Head heat loss is usually less than one-third to one-fifth of total heat loss. That means it is not the majority, which would be more than 50%. Head heat loss is usually less than 20-30 percent or so of total heat loss.
Head heat loss changes with how cold it is. The lower the temperature, the higher percentage head heat loss. Head heat loss is linear with temperature. At 0 degrees Centigrade, up to about 30 to 35% of heat could be lost through your head at rest.
Head heat loss changes with how much you exercise. When exercising at about a work rate of 50% of aerobic capacity, head heat loss falls to less than half of heat loss at rest.
