Basically, each textile offers a certain amount of UV protection. It is true: the denser the fabric and the darker the fabric, the higher the protection. Except that a heavy, black poncho isn’t everyone’s idea of comfy summer apparel. A dry, white cotton shirt just takes it to a UPF of 10, in wet condition the UPF melts down to 2.
Depending on the colour, fibre and weaving as well as the condition of the garment, the protective effect varies considerably. While a pair of jeans has a high protective factor, it is not a first choice to wear on the beach in summer temperatures. Light summer clothing offers virtually no UV protection due to its thin fabric, often bright colours and permeable weave. In addition, the UV protection of textiles is greatly reduced by moisture, stretching, abrasion and laundry, as the graph shows: