What does UPF mean?

The UPF rating indicates how effective a fabric is at blocking out solar ultraviolet radiation. UPF ratings range from 15 to 50 with higher ratings indicating more effective blocking and therefore better protection from the fabric. Fabrics that test higher than UPF 50 are rated as UPF 50+. UPF testing involves exposing a fabric to ultraviolet radiation (UVR) and measuring how much is transmitted through the sample. Different wavelengths of radiation in the UVR spectrum have different effects on human skin and this is taken into consideration when calculating the UPF rating.