TCRC Custom Design. Designed to meet the demands of race-day athletes, the F4 utilizes to provide compressed venting and moisture wicking in the most extreme conditions. Made with Sorbtek®, this sock channels moisture away from the foot, keeping it cool and dry. Anatomical left-right foot construction allows for precise fit, while a unique cushioning system provides comfort in specific pressure areas. Achilles protection reduces blistering on the back of the foot, and a front tab protects against shoe friction. The F4 is only available in no-show length.