Castellli Aero Race Pro 20 Sock Aero Where It Counts If you're building a race-day kit from the ground up, the sock is often the last thing on the list. The Aero Race Pro 20 makes a case for moving it higher. The structured aero ribs on the 20cm cuff sit in the Rosso Corsa tier, which means this is the sock Castelli puts on its fastest kit. The 90% polyamide blend keeps the fit close and the feel breathable, so it works on warm race days without turning your feet into a sauna. Features Rosso Corsa collection Castelli's top-tier designation, built for race-day performance Structured aero ribs textured cuff designed to reduce drag at road racing speeds90% polyamide / 10% elastane close, secure fit with all-day breathability20cm cuff height race-legal length that covers the lower leg for aero gain | Castelli | Aero Race Pro 20 Sock Men's | Size Large/extra Large In Belgian Blue