Newsletter XXII - What Makes Clothing Sun Protective?
Did you know that most regular summer clothing provides poor protection against ultraviolet (UV) radiation? In fact, many open weave, lightweight summer fabrics, like those used for T-shirts, provide less UV protection than an SPF 30 sunscreen. In addition, summer clothing styles are typically designed to expose skin, arms, neck, shoulders, rather than cover it. Sun protective clothing is therefore made with specialized fabrics that prevent UV from passing though the weave and designs that provide as much skin coverage as possible.
Factors Affecting UV Protection Levels in Fabric. A number of factors affect the level of ultraviolet protection provided by fabrics. In approximate order of importance these are weave (tighter is better), color (darker is better), weight (also called mass or cover factor, heavier is better), stretch (less is better), and wetness (dry is better). Adding chemicals such as UV absorbers or UV diffusers during the manufacturing process also creates UV protection in summer fabrics.
For many years people have sought sun protection in fabrics that are darker, heavier, and so on. Now, however, sun protective clothing is typically made from sophisticated, high-tech fabrics specially designed to be lightweight, cool, and easy to wear. For example, Coolibar's lite SUNTECT® is brightly colored, lightweight, and highly protective because it has a UV diffuser, titanium dioxide, built into the microfibers. And Coolibar's aqua SUNTECT® is a knit swim material that stretches but contains no Lycra, so holes do not appear as the fabric ages in chlorinated water. Both are part of a growing list of sophisticated sun protective materials that Coolibar tests and retests for maximum protection.
Testing for Ultraviolet Protection Factor. How do you know which fabrics provide good UV protection? In America, a fabric's UV protection is measured by an ultraviolet protection factor, or UPF. UPF is defined by the American Association of Textile Chemists and Colorists (AATCC) Test Method 183 as the ratio of UV measured without the protection of the fabric compared to with the protection of the fabric. For example, if a fabric is rated UPF 30, for every 30 units of UV exposure, only 1 unit will pass through the fabric. That material is therefore blocking or absorbing 29 out of 30 units of UV, or 96.7% UV. This kind of test is normally conducted in a laboratory with a spectrophotometer or a spectroradiometer.
AATCC 183, the test described above, should be used in conjunction with other related standards, including American Society for Testing and Materials (ASTM) D 6544 and ASTM D 6603. ASTM D 6544 specifies how to simulate the life cycle of a fabric so that a UPF test can be done at the end of that cycle, when most fabrics provide the least UV protection. ASTM D 6603 describes the appropriate way to label sun protective clothing based on the test results from AATCC 183. The highest recommended rating is UPF 50+. The best sun protective clothing will be rated UPF 50+ at the end of its life using AATCC 183/ASTM D 6544. At Coolibar, we carefully test using these recommendations and provide labels with our results.
Sun Protective Clothing Designs. Most summer clothing exposes large amounts of skin to the sun. A recent Coolibar study analyzed the skin coverage of typical summer tops sold in America. About 74% provided no protection for the lower arm, 64% provided no neck protection, and 16% provided no shoulder coverage.
A major goal for sun protective clothing designs is to cover as much skin as possible while still making the garment cool, comfortable, and fashionable. There is no formal rating system for the level of skin coverage provided by a garment, but maximum coverage provides the best protection.
What to Shop For. High-tech fabrics and maximum skin coverage are the key elements in sun protective clothing. Be sure to check labels for UPF test results, and look for styles that cover as much skin as possible.