OBG,
Just to clarify, I believe the article says that your head and neck amount to 7% of your bodies surface area, if you are shivering, that 7% sheds 55% more heat raising the actual heat loss from the scalp to about 10% of total body surface area which is the figure the article cites. Then to really confuse the issue, if you start sweating from the shivering, it drops back down to 7%. And yes, a hat still sounds good to me also...