The myth

You lose most of your heat through your head, so the most important piece of outdoor clothing is a hat.

The "truth"

Everyone knows this. Look at an outdoorsy website and you will be told it again, just in case you’ve forgotten it. But apparently, it’s not true. Anything from five to 55 per cent of a body’s heat loss can heat, and how much will depend to a great extent on how big it is (flashers be warned). Logically, if this myth were true, wearing a hat but no trousers would keep you warmer than wearing trousers but no hat: it won’t. (Flashers be doubly warned). Hypothermia expert Dr Daniel I Sessler of the University of Louisville medical school blames the belief on military experiments, using Arctic survival suits, conducted half a century ago. The suits did not cover the subjects’ heads, so of course most heat loss was from the top. Someone wearing just a swimsuit in cold conditions, says Dr Sessler, would lose only about 10 per cent of their heat via their heads.