9 days out of ten I just wear a thermal long serve under my jacket. Very comfortable, cheap, and warm. Blah, blah, blah moisture wicking, blah, blah, blah. Unless you don't know how to hike without sweating your balls off or like to shove snow down you jacket, cotton is fine. And I wear this in Colorado, where hikes take more than 7 minutes and it gets cold outside.