The UV protection factor (UPF) is used as the evaluation parameter for the UV protection performance of textiles. It represents the ratio of the average UV radiation effect calculated when the skin is unprotected to the average UV radiation effect calculated when the skin is protected by fabric.
GB/T18830–2009, "Evaluation of UV Protection Performance of Textiles," specifies the test methods, expression, evaluation, and labeling of the UV protection performance of textiles. The test principle involves irradiating the sample with monochromatic or multi-colored UV rays, collecting the total spectral transmittance t(λ), and calculating the UPF value. Parallel beams can be used to irradiate the sample, with an integrating sphere collecting all transmitted light; alternatively, a light hemisphere can be used to irradiate the sample, collecting parallel transmitted light. In practice, the testing instrument can automatically calculate the UPF value and t(λ) of the sample. When the UPF value of a sample is greater than 50, it is expressed as "UPF > 50." According to this standard, when the UPF of a sample is greater than 40 and t(UVA)av < 5%, it can be called a "UV-protective product."
