Not to be a party pooper - but...
I learned that 20% of all heat loss was through the head. However, I've also heard recently that those test results were skewed in that the person was dressed for the weather except for a hat, so of course most of the heat loss would be through the unprotected head area.
Can't remember where I saw that. But the article stressed covering all points where major blood flow is close to the skin (head, neck, groin) and the use of layers and no cotton.
I will try and figure out where I saw that.
On a related subject - I was a guinea pig -- uh-- test subject at the Natick research labs for a test to determine if people who have a certain condition - Reynaud's - can be helped.
Seems if you suffer from Reynaud's you can help alleviate the it by going outside in the cold not dressed for it, but place your hands in warm water for 10 minutes, go inside for 5, repeat 2x more and do this three times a week for 6 weeks you get some relief in that you get better blood circulation in your hands. Dunno how or why it works, just that it did.