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. Boot height, men’s sizes S (women’s 4-7) M(5-8) L(9-12) XL(13-15). Made in USA of 33% Merino Wool, 33% Polypropylene, 26% Nylon, 5% Elastic, 3% Lycra.