The Womens Smartwool PhD Running Ultra Light Micro Socks can go the distance without weighing you down. Combining athletic science and SmartWool quality, these PhD socks are some of the best athletic socks out there. These lightweight micro socks feature SmartWool cushioning in the critical impact zones for added protection and durability. The PhD Running Ultra Light Micro Sock was designed with SmartWool's 4-Degree Fit System, which works with the mechanics of the athlete's foot and has exceptional fit in critical areas. The Womens SmartWool PhD Running Ultra Light Micro Socks are perfect for those short to mid-length runs both on and off the trail.