The Solare fabric used in Castelli's UPF 50 Plus Light Leg Sleeves is a synthetic blend with a polyester base, so the Sleeves wick moisture and breathe like a more efficient layer of second skin. Unlike the actual skin they protect, though, the UPF 50 Plus Leg Skins protect against the harmful rays of the sun. Cyclists tend to spend a lot more time under the sun than other endurance athletes, so the added bit of protection is especially appreciated in the saddle. The Leg Sleeves' efficient moisture management also mean they keep you warmer in cool conditions, so they're ideal companions to pack in a pocket during long, July climbs and pull on to ward off speed wobbles caused by shivering during high-speed, chilly descents. Your legs are your engines; treat them well.