Hands,feet and facial extremities are the first victims to frostbite. Remember that a body will protect the core organs by shutting down circulation. It would be simple to say "keep warm," but there is more going on, with gear, our physiology and the environment. Most people venturing into cold or snow will have wool or pile socks and possibly a liner of poly or silk. This is about as good as it gets. What we put over it (boots) is where things can go wrong. Most boots are very robust affairs for wear and mechanical protection. leather, rubber and other manmade materials work well with various insulators- to a limit. Remember your body is pumping moisture out, and it either vents, or remains. Advocates of the Vapor Barrier school say this is a good thing. It works, until A. you remove the system for cleaning and B. the vapor overwhelms the ability of the insulation to absorb and the bodie's ability to warm become taxed. At @ 20 degrees snow becomes 'dry.' The system I prefer is a porous Muckluk of breathable canvas and leather. My foot is also in a flexible system that encourages mechanical heat and movement. The best of rigid boots become very unyielding affairs in extreme cold. Above 20 degrees external moisture is going to make a mess of things and another boot is required. A suprising strategy by Mors Kochanski can be seen and read @ www.countrywoolenmills.com