Well, the old saying on the survey crew was " if your feet are cold... cover your head".
I worked outdoors my entire career.. from many winters in Michigan to sub zero days in the Rockies, and I always suspected this advice was just BS. Now, covering my ears was a big deal but not so much my entire head.
To clarify this scary declaration by the scholars who spend most of their lives inside... I believe they are saying that when dressed appropriately, you lose a certain amount of your body's heat. When you head is uncovered, 1/2 of that heat loss is through your head. Now that's no surprise. I bet if you chose not to wear shoes, you would lose a similar percentage through your feet.
And I can guaranty you that if you feet are cold... nothing you put on your head will get them warm.
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