Castelli Climber's A/C Jersey Where the heat is high and the gradient is higher. CFD-based fabric placement is the starting point here, not an afterthought. Seam placement and panel geometry follow the same computational fluid dynamics process used on the Aero Race 8S, so the fit stays fast even when the road tips skyward. Flusso 3D fabric on the front pulls heat away quickly, while Strada Pro 3D on the back handles sweat and airflow over the long haul. Pair it with a base layer on a cool morning and it carries into shoulder-season territory without complaint. CFD-Based Seam Construction mirrors the Aero Race 8S layout to reduce drag without trading away ventilation on long, exposed climbs Flusso 3D Front Panel uses open 3D mesh to accelerate moisture evaporation and keep your core temperature in check during sustained efforts Strada Pro 3D Back Panel wicks aggressively and blocks over 90% of UV rays, so rear sun exposure on mountain roads stays manageable Airflow Shoulder Construction opens up ventilation at the top of the jersey where heat accumulates most during climbs Elbow-Length Stretch Sleeves with Raw-Cut Edges conform to the arm without bulk or binding, supporting an aerodynamic position in the drops YKK Vislon Zipper with Elastic Waist lets you dial ventilation on the fly while keeping loaded rear pockets from sagging on the descent | Castelli | Climber's A/c Jersey Men's | Size Small In Belgian Blue/winter Sky