I know while in my hammock that I usually cover my head with a balaclava or wrap a fleece scarf around it to help stay warm. I had always heard that most of my body heat is lost through my head. I read an article that said even the US Army is wrong in their survival manual when they recommend keeping the head covered in cold weather because "you can lose 40% to 45% of body heat from an unprotected head."
This myth most likely stems from a 50-year-old military study in which participants were exposed to extremely cold temperatures while wearing arctic survival suits that came to their necks. When heat loss was measured, most heat escaped from the head, which was the only part of their bodies not covered. Experts say that if you performed the same study on people wearing only bathing suits, they would not have lost any more heat proportionally from their heads than from any other part of their bodies.
So the head is not special when it comes to getting cold. Any body part that is exposed to cold weather will cause a drop in body temperature. I guess that's why we have UQ's and TQ's. My bald head still needs some type of covering.