windproof and breathable
I was skeptical about how warm this would be when it arrived and I noticed how lightweight it is. I was fully expecting to have to layer it under a fleece beanie. I was pleasantly surprised at how warm this thing is. I wore it climbing both Mt Kilimanjaro and Mt Kenya, with nothing over it. The winds were 30+ mph and temperature was sub-zero Fahrenheit. My head stayed nice and warm and I still hear pretty well. The material over the mouth allows for easier breathing then the typical "ski mask" variety, but sucking wind at 19K ft, I still had to pull it down when I needed deep breaths.
All-in-all, this is a terrific piece of cold weather equipment. (The packaging says you can also wear it as a beanie, but I found it to be too tight for that and wouldn't risk stretching it out to make it work. It's best used as a balaclava.)