Bontrager's SunStop Arm Covers are made with a fabric that's rated UPF 40+ to keep the punishing sun off your arms and ensure you stay cooler than riding without. They also wick and have mesh panels for excellent breathability.
I hate to get sunburn and these covers provide excellent protection and don't feel hot even on the warmest day. The wicking effect even makes for a cool effect as you ride. My wife has a pair and loves the coverage as well. Her's were a little loose on the upper arm.
