Wool is good. I've also had good luck with Polar Fleece, which is somewhat lighter. A Polar Fleece long-sleeve shirt with a vest of the same material under a shell is good down to minus 20F. Below 10F, I wear a pair of Polar Fleece pants over my work slacks, and a pair of nylon shell pants over both. With proper gloves and a balaclava I don't feel the cold. If I get too warm, I just open the zipper(s) on the things on top. My favorite socks are thick ones of a wool blend from REI.