Extremely lightweight and packable Aria 2 shell from Castelli is both breathable and durable and designed for days when the weather does a little bit of everything. And what's really unique is how they use the stretch panels in the sides and on the back of sleeves to make the Aria fit like a second skin. No flapping, no cold air circulating inside, folds into its own side panel pocket and stuffs away in your jersey pocket or seat bag. Best used in temperatures of 50-65 degrees and meant to be worn very fitted. Athletic fit.