I thought I'd give these a try versus the standard cotton ones.  The poly fabric is very thin and breathable which I am sure it is perfect for runners and anyone doing constant outside physical activity.  But if you want something to keep the heat in while you are standing outside waiting for the train, you are still better off with heavy cotton.  All of those holes in the poly fabric means "heat lost."  Also I wast thrilled with the fit -- they would slide down a few inches and I'd have to pull them up. My flannel lined jeans and cargos from LLBean are the better bet, for me at least.