Castelli Fast Feet 2 Socks This Sock Saves Watts If you want to be too swift on your toes to get caught up being slow, then you might want to consider a new pair of racing socks. The Castelli Fast Feet 2 Socks are aerodynamic socks that can help you save watts while racing. The foot portion is based on the Castelli Rosso Corsa Sock for in-shoe comfort and the leg portion is constructed with engineered grooved Lycra to help detach airflow. With the polyurethane grip strip at the top of the sock, your socks will stay in place while you're riding. Features The foot portion is based on the Castelli Rosso Corsa Sock for in-shoe comfort The leg portion is constructed with engineered grooved Lycra to help detach airflow Polyurethane grip strip at the top to keep the sock in place Sizing Size Small/Medium Large/Extra Large XX-Large US Shoe Size4 - 78 - 1011 - 14Men's Euro Shoe Size36 - 3940 - 4344 - 47 | Castelli | Fast Feet 2 Sock Men's | Size Xx Large In Black | Polyurethane