As for the “myth” about putting on a hat when your feet are cold, I sincerely doubt that it’s so cut-and-dry.

For one, if you’re cold, a large majority of your warm blood will be constricted into your core and head. So, where exactly are you losing most of your heat then? It may be true that you lose heat evenly when your body temperature is normal, but once your body temperature starts dropping, you’ll lose more heat from where the blood concentrates. If your feet are cold, it’s probably because the blood went somewhere else.

Secondly, I’ve seen only a little bit of discussion about hair. If you’re considering surface area to be the most significant factor, your hair increases your head’s surface area dramatically. In calm weather, your hair may be able to create a nice insulating layer. In more harsh weather, where this “myth” actually comes to practical use, the wind will be blowing your hair around so much that it may actually start acting as a heatsink.

Somehow I find more credibility in the various thermal images I’ve seen showing people in cold weather. These images normally show people in winter clothes as a dark colored body with a big, bright spot depicting their head. So, where are they losing the most body heat from then? This “myth” needs to be looked at in the big picture, as applied to people who are in a survival situation and are cold. If the norm for this scenario were to be naked, then maybe the difference in heat loss between your head and the rest of your body wouldn’t be significant. However, being naked is not the norm, and if you’re naked in the cold, you have bigger problems that to grab a hat. The myth simply means, in all its glory, “Don’t forget your hat.”