Castelli's latest version of its slippery top, the Aero Race 6. 0 Full-Zip Jersey, is the culmination of everything it's learned about material and design and is distilled into its fastest jersey to date. The jersey is optimized at the real-world speeds we often find ourselves riding (18 - 34mph) and the human body makes up the majority of watt-sucking drag on our rides. This sixth revision of its aero jersey is more aerodynamic and better fitting than ever, by optimizing fit, paneling, and seam placement. The fabrics used provide superb breathability and ventilation, to help ventilate while you're pushing the pace.