Smartwool PhD? Outdoor Light Pattern Mid Crew, Black, Large 61% Merino Wool, 36% Nylon, 3% Elastane Light Cushion: The ideal cushion for varied trail and road terrain. Mesh Venting: Men's-specific mesh ventilation zones provide additional breathability and moisture management. PhD = Built for Performance in the Highest Degree. 4 Degree Elite Fit System: Uses two elastics for greater stretch and recovery to keep the sock in place. ReliaWool: Patented ReliaWool technology in high impact areas provides superior durability. Strategically placed mesh ventilation zones provide ventilation for temperature and moisture management Sock Height: Mid Crew: 6" overall height - Flat knit durable toe seam Style: SW0SW218 - Knit in USA of Imported Yarn