The PhD® Run Ultra Light Micro Sock features a run-specific fit with the 4 Degree elite fit system, which uses two elastics for greater stretch and recovery. Patented ReliaWool technology in high impact areas increases durability. It has mesh ventilation zones, a virtually seamless toe, and an achilles tab. 54% Merino Wool, 42% Nylon, 4% Elastane. If you're not fully satisfied with your purchase, you are welcome to return any unworn and unwashed items with tags intact and original packaging included. Made in: USA