Ultraviolet Protection Factor (UPF) measures the amount of UV radiation that penetrates a fabric and reaches your skin. A fabric rated with a UPF of 50 will allow only 1/50th of the sun’s UV rays to pass through. In other words, it blocks 49/50ths or 98% of the UV radiation. UPF 50+ is the highest possible rating. Samples of fabrics have been tested for UV protection by LEITAT—Textile Technology Institute in accordance with the standard AS/NXS4399:1996 “Sun protective clothing--Evaluation and Classification."