Why? I would have thought leaving a baby with nothing on their head when its barely 5 degrees is riskier ... really little babies are mostly head and that's a lot to leave uncovered. The day we had a stupidly long power failure he was in 3 layers, hood, hat, AND a regular adult quilt on the couch and we were barely warm enough.

Probably not so much of an issue where its warmer though ... we get Canberra weather here, without the snow.
We were told not to leave a hat on bub unless we were watching him because we use our heads to regulate temperature... with a hat on they can't let excess heat escape...

OP - my bub's hands and feet aare always cold, but I know when we were in hospital they said bub's can reduce blood flow to these areas to help maintain body heat. But as others have said, if you are comfortable then bub will be. I have bub in a Bonds wondersuit, cotton wrap, then a sheet and cot blanket... he doesn't move all night and is quite content