Anything but cotton and that includes the upper body as well. I agree with Jigginstick....polypro liners and good wool socks works for me. I also go with just wool socks sometimes, keep them loose,not to snug and I never lace up my boots tight. Before I saw the light I use to wear several pairs of socks at one time including cotton to try and keep warm. That only cuts circulation to the feet plus the cotton doesn't wick the moisture away from you feet. If you don't have polypro then go with straight wool. It will will keep you warmer than cotton even if the wool gets wet.
