Polypropylene is the hottest thing in thermal underwear on the market! This government issue 100% polypropylene is 1/16 in. thick with a fleece texture next to your skin. Our troops use these long johns with their extreme cold weather gear. Polypropylene is designed to wisk away moisture from your skin to keep you warm and dry. All new. Shirt has a high neck collar with a 12 in. zipper. Snug 2 in. cuffs on sleeves. No waistband. Sizes M (chest size 38 to 40 in.), L (chest size fits 42 in. to 44 in.), XL (chest size fits 46 in. to 48 in.) We also have the polypropylene bottoms.