These 100 % polypropylene long johns are awesome. I found out about this fabric in the 80s, and bought some bottoms for winter, back then I paid 36 $ a piece for them,  And Im here to tell you they are super thin, almost like a second skin. I would ride my bycicle in the winter when it was 10 below and colder ! As these for a base layer and just a pair of jeans on these underwear retains your heat and keeps you very warm. You would never think a fabric this thin could keep you so warm. And to fimd these 100 % polypropylene for 11 $, I bought 2 pairs !!!!!!