I use them for work, I'm a locksmith and sometimes I work outside in the bitter winter cold. They are quite expensive but definitely worth the price in the end. in all sizes, I have medium and L. The material is very stretchy and even if you order a size smaller it will most likely fit you after a few uses and a good wash in cold water. I've been wearing it for 10 years. The weather is -15F for 6-8 hours and I can say it will keep you warm no matter what, in fact I do feel a bit sweaty if I move too much wearing this under my work clothes ! The material is very thin, but like Under Armor always takes care of it when you need to generate/store body heat! This is a very good product, made from the highest quality materials (which is what most UA products are made of), also I have a couple of UA sweatshirts with the same warm quality and thin material design and am enjoying each one to the fullest! 5 Stars !