As some have mentioned, keep room in your shoes for the warmth to flow. If they're too tight they cut off circulation which doesn't allow the blood to flow in your feet. Get a good pair of thinner wool socks - smartwool works pretty good. Layer outside with a thin wicking coolmax sock - there's a certain brand at Target which are really thin and black ankle socks. Excellent. They're perfect with my Diadora Gekos (mesh top and sides) in the 30's. Below that I use some neoprene toasties (booties for the toes only) from Performance that I got for $10. MY feet are thus fine.