Improving sun protection factors of fabrics by applying UV-absorbers

Designing and modifying fabrics in such a way that they offer high protection against UV-light (''UV-cutting'') is a relatively new application. Thin, untreated fabrics made, for example, from cotton, silk, polyamide, and polyacrylonitrile offer sun protection factors (SPF) only in the range of 3 to 5, i.e., their UV-cutting effect is inadequate when the sun's irradiation is intense. The SPFs of fabrics can be increased in a variety of ways, using thicker fabrics or applying UV-absorbers. In this article we are presenting a model that makes it possible to predict SPFs of fabrics as a function of a diversity of parameters, such as fabric type, thickness, and porosity, as well as UV-absorber (or dye or optical brightener) type and concentration. Important parameters for achieving high SPFs are identified. The model is confirmed by experimental data. We also provide data about how long it takes until reddening of unprotected skin is observed under various conditions.