Okay here’s the answer, and the history behind the misconception. The answer is it’s dependent on exposed surface area, meaning that if you cover yourself head to toe, your head would account for about 7%-10% body heat lost

Muahaha, tricked you guys. It’s true though that it’s often cited that anywhere from 40% to 80% of your body heat is lost through your head, often followed by your parents telling to you put on a hat. This actually comes from a misinterpreted study. A study done by the US military found that in the study, 40%-50% of the body head lost was lost through the head. What was later ignored was the fact that the subjects were completely covered with thermal military attire except for the head. Later, the number was inflated massively, reaching as high as 80% in the claim. And you can logically notice the dilemma here. If your head loses 60%-80% of your body heat, that would mean that you’re better off wearing a hat, scarf, and nothing else but underwear, than if you wore a shirt, sweater, coat, gloves/mittens, warm pants, snow pants, warm socks, and boots, but no hat. After all, in this case, the part of you that supposedly loses the most heat, the head, is fully covered.

this isn’t to say you shouldn’t cover your head. You should if it’s really cold, and it’s definitely the area people tend to ignore most when dressing for cold weather. But not because you lose almost all heat though your head