By fusing together low-micron merino wool and polypro fibers you get an incredibly strong yarn that allows a middleweight to act like a heavyweight in both warm and cold climates. They're strong wicking odor and blister resistant breathable quick drying..... and they immediately recover in the wash. When the weather is a little less extreme on either end of the spectrum reach for these. Made in USA of 33% Merino Wool 33% Polypropylene 26% Nylon 5% Elastic 3% Lycra. Men's sizes M(5-8) L(9-12) XL(13-15).