Although most armbands are designed to keep you warm Castelli's lightweight UPF 50 arm guards can actually keep you cool, too. They are rated UPF 50 , however Castelli claims that in laboratory tests they actually blocked 99 8 percent harmful ultraviolet rays. It is based on polyester which blocks ultraviolet rays more effectively than regular nylon while maintaining dryness. Minimal seam design prevents chafing , and double-sided silicone rubber in the holes guarantees that they will remain in place throughout the trip. Besides They are very compact so you can put them in your jersey pocket when they are no longer needed during the day.