After running last night and abusing my bare cheeks in the cold wind, I decided to look for a bit of scientific information to help me determine when coverage is needed to prevent frostnip/frostbite. Here is a link to the Environment Canada web site where they did a very scientific study on when your skin will freeze, something very appropriate for mountaineers to know. Keep in mind that frostbite at altitude is more likely because of reduced oxygen.

Jim

http://www.msc-smc.ec.gc.ca/education ... chill/research2003_e.html