i own a set of hot chillys single ply long underwear for a year now, and i simply love them. they're loose in the right spots and fitted in the right spots. they're good down to about 30 degrees, and i couldn't be more satisfied. this year i bought tops and bottoms of hot chillys bi-ply. these are in another league altogether and have become my favorite base layer. they are warm, but not overly so. it seems like they adjust to the outside temperature and i have nothing but rave reviews for the bi-ply. 5 stars.