Castelli's latest version of its slippery top, the Aero Race 6. 0 Full-Zip Jersey, is the culmination of everything they've learned about material and design distilled into its fastest jersey to date. The jersey is optimized at the real-world speeds we often find ourselves riding (around 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 provide superb breathability and ventilation to aid airflow while we're pushing the pace.