Unless they are very large, umbrellas provide relatively little UV protection. Their SPFs can range from 3–106 and their UPFs up to 50+ (UPF, the ultraviolet protection factor, measures protection from UV radiation in fabrics. A shirt with a UPF of 30 indicates that just 1/30th of the sun’s UV radiation can reach the skin), but no matter how high the fabric’s SPF or UPF, the amount of UV present beneath an umbrella can be up to 84 percent of that in sun7 depending on the levels of indirect UV; the amount of indirect UV is proportionate to the amount of open sky visible from the shade.10 Therefore, a single umbrella on a sandy beach by the sea provides limited sun protection because so much UV is reflected under the umbrella from the surfaces of the sand, water and sky