The Castelli UPF 50+ Arm Skins prevent the sun's rays from damaging your skin. Sunny days can feel like a curse. Not having to bundle up is nice, but slathering on sunscreen is tiresome, yucky, and can result in allergic reactions. Going without can lead to burns, premature aging, skin cancer. You don't want to look like a leather handbag until well after you start drawing on Social Security. To keep the sun off your guns on hot days, these skins have to do two things. One is really keep it off, better than sunscreen. The second is keep you as cool as possible for a covering. Castelli chose to employ Solare fabric to take care of both tasks. The material has a UPF, Ultraviolet Protection Factor of 50+. This means the material allows or 1/50th of the solar radiation hitting the garment to get through-or, if you prefer to think positively, it stops 98% of the solar radiation from getting past the material. The second feature of the Solare fabric is the sheer quality of it. It's thin, really thin. And it's polyester-based, so it wicks without absorbing. It fits like a traditional Castelli arm warmer. The top has a two-sided silicone-beaded elastic, which both grabs your sleeves and your biceps. The bottom has a doubled-over hem. The Castelli UPF 50+ Arm Skins are for the days when you don't want the kiss of nature to show.