Lots of arm coolers promise to protect you from the sun. Now you have arm coolers that remind you to keep cool. You’ve seen the so-called cooling fabrics on the market for a few years now. Those fabrics are infused with Xylitol which your skin perceives as being cool, although it actually does nothing to actually cool you. The actual cooling still comes from evaporation.Castelli’s Chill Sleeves are made with our new Prosecco Ice fabric. It’s got its Xylitol so it feels cool so you still get your placebo effect. But it also has the heat-sensitive Castelli print that turns invisible as it warms up. That’s a visual reminder to you to pour some water over the arm coolers to keep them moist. The nylon based fabric will hold the moisture for maximum cooling as it evaporates. It’s UPF 50 protection keeps the UV rays out.