Built light for those epic days with lots of climbing and heat, you can count on the Climber's 2. 0 Full-Zip Jersey from Castelli to keep you cool. It doesn't ignore aerodynamics either thanks to its patterning that's similar to the Aero Race 6. 0 Jersey, so you end up with a jersey that's cool and light, and it's no wonder that it's a favorite among its sponsored riders. Castelli uses its lightweight StradaPro 3D polyester and Flusso 4D mesh to make the jersey as breathable as possible when you're riding on hot, energy-sapping days. The whisper-thin fabrics keep sweat moving off your skin so you stay as dry and cool as possible while climbing.