Originally Posted by
FBinNY
I've never had an issue with my head getting cold when cycling, regardless of temperature. The exercise heats the blood, and it heats the head. Even my ears do OK except maybe on descents.
My problem is warming the air that I breathe, so my nose and the sinus area can get pretty uncomfortable, but that's about it.
I suppose it depends on the temperature you ride at. Back in the day I had to opt to ride helmet free (even mountain biking) because i could not fit enough insulation under the helmet. But we're talking -10 to -40 celsius. Never had sinus issues though.
Nowdays I have a POC Fornix winter sport helmet which lets me cycle in conditions where I'll freeze my bearing grease before my head gets cold.