Measuring the UV Protection Factor of Fabrics

Sun protection fabrics are designed to absorb or reflect the sun’s UV radiation as a means of protecting the skin from damage. The rating system for fabrics specifies an Ultraviolet Protection Factor (UPF) value, which can be thought of as a time factor for the protection of Caucasian skin compared to exposure without any protection. For example, if a person would show visible erythema (sunburn) after five minutes of exposure, fabric with a UPF of fifty extends that time to five minutes times the protection factor, i.e. 250 minutes, or roughly four hours. Scientific methods of evaluating the UPF of fabrics have been developed and specified according to Australia/New Zealand (AS/NZ) standard 4399:19961; other nations and regions have produced their own standards modeled after this original work, e.g. AATCC 183:20042 with ASTM D6544 and ASTM D6603 in the United States and EN 13758-1 in Europe. The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) maintains an excellent website3 with many details concerning UV protection and monitoring. A summary of the requirements of the various standards, reproduced from that website4, is included in the gray box on the following page. The standards call for diffuse transmittance measurements obtained on a UV-Visible spectrophotometer equipped with an integrating sphere accessory. The AATCC 183:2004 standard specifies that the integrating sphere used must have a port fraction no greater than 3%. This requirement eliminates most smaller (< 150 mm) spheres on the market from consideration for use in this application. The Thermo Scientific DRA-EV-600 75 mm sphere, however, has a port fraction of 2.86% when configured for transmission measurements, so it is compatible with this standard. The methods also require that a fluorescence filter such as a Schott UG11 be placed between the fabric sample and the integrating sphere. Brighteners, i.e. chemicals included in certain fabric dyes that absorb in the UV and fluoresce in the blue, have the potential to cause erroneous measurements of UPF by making transmission appear high. Inclusion of the fluorescence filter overcomes this problem. This application note describes the measurement of UPF using a Thermo Scientific EvolutionTM 600 UV-Visible spectrophotometer, a DRA-EV-600 Integrating Sphere accessory with fluorescence filters, and VISIONliteTM MaterialsCalc software. Background