UPF 50+ Summerweight Sun Protection. The essential accessory for protection against UV rays that lasts all day. Sun sleeves provide weightless protection at UPF 50+ that will last all day and actually have a cooling effect when you put them on! These fabric sleeves mean there's no need to apply and reapply sunscreen. The super-soft sun sleeves will keep you protected all day long. Features + Benefits UPF 50+ protection Cooling fabric Light elastic gripper at top of the arm Breathable and fast-wicking Made in Italy Learn More What is UPF? Similar to the SPF of sunscreen ratings, UPF (Ultraviolet Protection Factor) measures the effectiveness of sun protection in fabrics. A UPF rating indicates how much solar radiation penetrates to reach the skin. A fabric with a rating of 50 allows just 1/50th of the sun’s rays to pass through, reducing skin exposure by blocking 98% of UVA and UVB rays. Sizing In general for warmers, match your typical apparel size. If you have a slim build, we recommend sizing down, or if you have a larger build, size up. The following measurements (in inches) are of the actual garment, laid flat. XS S M L XL INSIDE ARM 16.0 16.5 16.9 17.4 17.9 OUTSIDE ARM 18.7 19.3 20.0 20.7 21.3 WRIST CUFF, 1/2 2.5 2.7 2.9 3.1 3.3 UPPER ARM CUFF, 1/2 4.3 4.6 5.0 5.3 5.6