Our best fitting, most advanced run socks yet, we packed years of testing, prototypes and running smarts into these socks. Featuring Light Elite cushioning in the ball and heel of the foot for ultimate shock absorption with minimal in-shoe volume, men’s-specific mesh ventilation zones and a virtually seamless toe.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.