The UPF (ultraviolet protection factor) is a numerical rating given to clothing to indicate how effectively the fabric blocks ultraviolet (UV) radiation. A UPF rating of 25 means that only 1/25th (or 4%) of the UV radiation can penetrate the fabric. Unlike SPF, which only expresses a sunscreens protective value in terms of limited wavelengths of light, UPF applies to a range of broad spectrum UVA and UVB radiation. The highest UPF rating a garment can be assigned is 50+. A piece in this range is determined as providing 'excellent' protection from UV radiation.