I had been getting a cold head lately as my bike helmet is too well ventilated for winter, but putting a hat on meant the helmet no longer fitted.
This balaclava is thin but very windproof and warm and allow my helmet to still fit with no adjustment:
BLACK WINDPROOF MOTORCYCLE MOTORBIKE BIKE HELMET THERMAL WINTER BALACLAVA | eBay
This balaclava is thin but very windproof and warm and allow my helmet to still fit with no adjustment:
BLACK WINDPROOF MOTORCYCLE MOTORBIKE BIKE HELMET THERMAL WINTER BALACLAVA | eBay