SmartWool Men's Phd Run Ultra Light Micro Socks 54% Merino Wool, 42% Nylon, 4% Elastane Knit in USA Ultra Light Cushion: Minimal cushioning for maximum next-to-foot performance without added bulk. 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. Mesh Venting: Men's-specific mesh ventilation zones provide additional breathability and moisture management. 200 needle construction provides highest knit density while maintaining ultra light weight. Virtually seamless toe/ Achilles tab Sock Height: Micro - 1.5" overall height Style: SW0SW148