Designed for climbing on the hottest days, the Castelli Climber's 3. 0 SL 2 Jersey maximizes airflow to keep us cool when the sun shines directly down on us. On the back of the jersey is StradaPro 3D fabric which is engineered to block over 90% of UV rays, while the Flusso 3D fabric on the front and sleeves keep things aerodynamic and airy.