Helmet Cap 400
This hat is good for any activity requiring full peripheral vision in temperatures ranging from 5 to -15 degrees Celcius. Ideal for any activity where lightweight warmth is needed under a helmet—ice climbing, biking, horse back riding, etc.. The Woolpower Helmet Cap is made from their 400 weight wool. Woolpower has added terry loops on the interior of their products which they call Ullfrotte. This adds in the warmth as it helps traps air, and thus maximize insulation. To start a couple points… Full review
Woolpower makes warm, insulating base-layers, mid-layers and socks.