The head does not lose 80% of body heat

The share of heat lost through the head depends on which body areas are exposed, clothing, temperature, and conditions. The head is only part of the body’s surface; if the rest is clothed while the head is uncovered, its contribution can appear disproportionately large. In a cold-water immersion study, the head did not lose relatively more heat than the rest of the surface under comparable conditions. Thus, 80% is not a general physiological constant. A hat can still reduce heat loss from an exposed area in cold weather.