Smartwool PhD Outdoor Light Medium features Reliawool Technology for improved durability in the high wear areas and the 4-Degree Elite Fit System, to keep the sock in place and giving you all-sport versatility. Knit in USA of 64% Merino Wool, 34% Nylon, 2% Elastane  New 4 Degree Elite Fit System uses two elastics for greater stretch and recovery to keep the sock in place  Patent pending ReliaWool Technology in high impact areas provides the longer lasting protection to keep feet comfortable  Strategically placed mesh ventilation zones provide ventilation for temperature and moisture management  Flat knit durable toe seam for high burst strength  2x1 ribbed welt  1x1 ribbed leg  8.5\" overall height