These leggings are great as a base layer, or as athletic leggings. They fit as expected through the legs and waist and are stretchy. My only complaint with the sizing is that there isn't enough room in the back, they tend to come down a little bit when doing running, biking, etc. I don't think that would really be a problem though if you are just wearing these as a base layer. I wore them under my jeans at night while camping and they kept me super warm, and I wore them by themselves during the day and I was still very warm. For reference, I am 5'4, 140 lbs, athletic build and usually a Medium. I got these in a Medium.