These are the bomb. I live in Alaska and know what I am talking about. This layers well with other garments. The pants version of this top runs much smaller than the shirt. I am 5'9" and weigh 155, the medium fits but I bet the small would have fit me a little tighter for a fully conforming first layer. Couple this with some merino blend leggings and a pair of insulated Carhartt pants and you are almost ready for winter.