Ultraviolet Protection Factor
Just like sunscreen, the sun protectiveness of clothing can be evaluated and rated with a measuring system called Ultraviolet Protection Factor (UPF). UPF is a similar concept to SPF; however, UPF rates both UVA and UVB protection, whereas SPF only rates UVB protection. In 1996, the term UPF was devised in Australia as a measure of how much UV penetrates a fabric.
UPF is determined by using a UV transmittance analyzer to gauge the spectral transmission of UVB and UVA through a fabric. If a fabric is rated UPF 30, then it is absorbing or blocking 29 out of 30 units of UVR, or 97 percent of UVR. This is the same level of protection provided by an SPF 30 sunscreen that is used properly. To achieve a UPF, a fabric must undergo 40 simulated launderings, be exposed to the equivalent of 2 years of light exposure and be tested with chlorinated water if it is intended for swimsuits.
Specially Made Sun Protective Clothing
Today, many manufacturers offer special UV-absorbing clothes, from swimsuits and shirts, to hats and pants. This clothing will usually have a high UPF rating, indicating how much UVR it absorbs. These clothes have special weaves, and are treated with UV-absorbing chemicals such as titanium dioxide.
To be deemed sun-protective, such clothing must have a UPF of more than 30 and retain its sun-protective qualities after numerous washings and exposure to sunlight.