What is the difference between UPF and SPF?

UPF (Ultraviolet Protection Factor) and SPF (Sun Protection Factor) are both measures of sun protection, but they differ in the way they are calculated and the type of radiation they address. UPF is used to evaluate the effectiveness of sun-protective fabrics, while SPF is used for sunscreen products. UPF measures the fabric's ability to block UV rays, considering both UVA and UVB. It indicates the amount of UV radiation that can penetrate the fabric and reach the skin. SPF, on the other hand, measures the time it takes for UVB rays to cause skin redness when wearing sunscreen, compared to unprotected skin. Although UPF and SPF are related concepts, it is important to understand that they assess different aspects of sun protection to ensure comprehensive shielding against harmful ultraviolet radiation.