The Smartwool PhD Run LE Micro is the best fitting, most advanced run socks. This sock features 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 SeamlessTM toe. The micro height sock includes body-mapped mesh zones for added breathability. The Achilles tab is designed to prevent the sock from slipping down into footwear. It comprises of 56% Merino Wool, 41% Nylon, and 3% Elastane.