Laboratory testing of UV transmission through fabrics may underestimate protection.

Laboratory testing of the ultraviolet protection factor (UPF) provided by fabrics normally utilizes a collimated source of UV radiation and either a broadband sensor or spectroradiometer to detect the radiation, both unattenuated and after passing through the fabric sample held in a flat tensionless state. We report the results of an in vivo study of UV transmission through various T-shirts at several sites on the trunk and arms of a life-size mannequin irradiated with diffuse radiation and using UV sensitive polymer films as the sensor. We found a variation in UPF by a factor of two or more at different anatomical sites for a given T-shirt, with lower UPFs seen at sites where the fabric is stretched; and found that at every site and for each T-shirt this in vivo UPF was higher than the conventional in vitro UPF determined using collimated radiation.