SmartWool PhD Outdoor Light Mid Crew Sock 67% Merino Wool, 31% Nylon, 2% Elastane Knit in USA of Imported Yarn Light Cushion: The ideal cushion for varied trail and road terrain. Mesh Venting: Men&#39;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. 67% Merino Wool, 31% Nylon, 2% Elastane Strategically placed mesh ventilation zones provide ventilation for temperature and moisture management Sock Height: Mid Crew: 6&quot; overall height - Flat knit durable toe seam