Castelli's Fast Feet project: aerodynamic foot coverings for every condition. The Fast Feet Sock provides an aero advantage for road racing when it's too warm for the faster shoecovers. We take the leg portion of our TT shoecover and stitch it to our most comfortable sock for in-shoe comfort. It's the same as the aero sock we supply to our pro athletes, and it's a riders' favorite. Also available for customization in our Servizio Corse program.