1000 Mile Racer Mid-Height Running Socks Moisture-managing yarn mix - Wicks sweat to keep you dry and comfortable. Top vents - Increase breathability. Arch bracing and Y-heel - For additional support and a custom fit. HeelPower design - Grips the heel to reduce slippage. Fabric - 65% polyamide, 34% Tactel, 1% Lycra.