Peter Gies, PhD
Senior Research Scientist
Ultraviolet Radiation Section Non Ionizing Radiation Branch
Alan McLennan, NZCS
Senior Technical Officer
Ultraviolet Protection Factor Testing Service
Australian Radiation Protection and Nuclear Safety Agency
Yallambie, VIC, Australia
In 1990, after discussions with the Cancer Council Victoria (CCV) regarding how much ultraviolet radiation (UVR) protection was provided by clothing, the CCV purchased a number of items of summer beach wear and sent them for testing to the Australian Radiation Laboratory (later renamed ARPANSA, the Australian Radiation Protection and Nuclear Safety Agency). The test results were surprising, with only a few of the garments achieving a Protection Factor (PF) against UVR greater than 15. This was somewhat comparable to a sun protection factor (SPF) of 15 on sunscreen (at that time the maximum SPF in the Australian sun- screen standards).
Solar UVR levels in parts of Australia often reach extreme UV Index levels in summer,1,2 and the clothing ideally should have had PFs of at least 40-50 for adequate all-day protection of people with fair skin. The low PF levels found on the tested garments inspired a testing program to seek fabrics and materials providing proper sun protection that could be wholeheartedly recommended to the general public, outdoor workers, and schoolchildren in summer.
UPF: The Ultimate Measure of Clothing Sun Protection
A major step in the right direction was development of the ultraviolet protection factor (UPF) measurement, standardized in Australia in 1996.3 Based on a laboratory test of the amount of UVR that penetrates fabrics, the measurement quantifies how effectively a piece of clothing shields against the sun, depending on traits including the fabric’s content, weight, color, and construction. Since an item of clothing scatters much of the incoming UVR, the test method uses an integrating sphere to capture all of the direct and scattered UVR passing through the clothing. It also employs a spectral measurement system to quantify the amount of UVR transmitted through the fabric at each wavelength across the UV range, since shorter wavelength UVB is about 1,000 times more effective at causing sunburn than longer wavelength UVA.
The term UPF was adapted in lieu of the well-established sunscreen SPF measurement for specific reasons.3 First, the UPF measurement is based on an in vitro test, and the desire was to distinguish it from the SPF test, which is performed on live subjects. Second, UPF signifies both UVA and UVB protection, while SPF is specifically a measure of UVB protection (though broad-spectrum sunscreens with SPFs of 15 or higher protect substantially against both UVA and UVB). A shirt with a UPF of 50, for example, allows just 1/50th of the sun’s UVA and UVB rays to reach the skin. Third, the lab UPF test better reflects real-world protection than SPF does. To achieve reason- ably accurate test results for sunscreens, the testing thickness is much higher in the lab than what is generally applied outdoors, and substantial research has shown that people rarely apply sunscreen correctly, typically missing spots and failing to apply sufficient amounts. Thus, SPF measurements in the lab are rarely achieved in actual practice.4 In contrast, clothing tested in the lab may actually have a lower UPF measurement than when it is worn outdoors. Laboratory UPF testing simulates a worst case situation, where the UVR is incident at right angles to the fabric and transmission is therefore maximal. In general wear situations, clothing often provides protection in excess of the UPF rating because the incoming UVR will be at a range of different angles and only at right angles a fraction of the time. Thus, when consumers see a UPF label on an item of clothing, they can be confident about the listed level of protection.
In studies done in Australia, lycra/elastane fabrics were the most likely to have UPFs of 50 or higher, followed by plastic, nylon and polyester.5 They provide excel- lent sun protection, in contrast to, e.g., a thin white cotton T-shirt, which has a UPF of about 5, allowing 1/5th of the sun’s UVR to pass through—even more when wet. To date, ARPANSA has tested more than 28,000 fabric samples. The most commonly tested types of fabrics are shown in Table 1, along with their rated UPFs.
In general, clothing often worn outdoors in high-UVR regions should have a UPF of 50+. This would include, for example, school uniforms and schoolwear, workshirts, high- visibility shirts and vests, swimwear and rash vests (aka rashguards, which usually should exceed UPF 50+ by a considerable margin because their UPF decreases when wet), fishing clothes and associated gear, and police uniforms.
Today, systems for testing and determining UPF are similar around the world. In many countries, including the US, the ASTM International (formerly called the American Society for Testing and Materials) criteria for UPF assessment are used; UPF labels in the US often state that an item meets ASTM International standards. Clothing with a UPF of 30 or higher can also earn The Skin Cancer Foundation’s Seal of Recommendation.
Clothing Traits that Determine Sun Protection
To be absolutely certain of an item of clothing’s sun-protective ability, the item has to be UPF-tested. However, in the real world to date, only a limited number of (often designer) clothing items come with UPF labels. Unfortunately, it is difficult to tell how protective clothing is by looking at it or holding it up to the light, because the human eye responds to visible radiation and not to UVR, and the transmission of fabrics in the visible range is often higher than in the UVR range. Even when a clothing item appears to allow little light through, excessive UVR may be penetrating.6
Thus, consumers need to consider several key factors when seeking to purchase sun- safe clothes. First, at the most fundamental level, the more skin you cover, the better. A long-sleeved shirt covers more skin than a T-shirt, especially if it has a high neckline or collar that shields the back of the neck; long pants cover more skin than shorts. A wide- brimmed hat protects more of the face than a baseball cap, and close-fitting wraparound sunglasses protect more of the area around the eyes than small lenses do.
However, no matter how much clothing you wear, if the sun penetrates it easily, it’s not protective. Fabrics are made of tiny fibers woven or knitted together. Under a microscope, we see spaces between the fibers; UV can pass directly through these holes to reach the skin. The most important single protective factor of fabrics is cover factor or weave density – i.e., how much of the fabric is actually fiber and how much is open space, through which UVR can pass. (See Figure 2.) The tighter the knit or weave, the smaller the holes and the less UVR can get through.
Composition of the fabric fibers is also very important, as some materials strongly absorb UVR while others transmit more UVR. Most fibers naturally absorb some UV radiation, and some have elastic threads that pull the fibers tightly together, reducing the spaces between the holes. Synthetic fibers such as polyester, lycra, nylon, and acrylic are more protective than bleached cottons, and shiny or lustrous semi-synthetic fabrics like rayon reflect more UV than do matte ones, such as linen, which tend to absorb rather than reflect UV.
Other key factors include:
- color: Darker colors absorb more UVR than lighter colors of the same material, including whites and pastels, but bright, vivid colors such as red can also substantially absorb UVR.5 Many dyes absorb UVR, which helps reduce exposure, and many white fabrics have “optical whitening agents,” chemical compounds that strongly absorb UVR, especially UVA.6,7
- weight per unit area and fabric thickness: Heavier, thicker clothes absorb more UVR. For example, light, sheer silk gauze provides far less UV protection than heavy cotton denim.
- tension or stretch: More stretch lowers UPF rating.
- moisture content: Many fabrics have lower ratings when wet; for example, the UPF of a thin white cotton T-shirt may decrease from 5 to only about 3 when wet.
- fabric condition: The more worn and frayed clothing is, the more UVR it lets through.7
Conclusions: Dedicated High-UPF Clothing vs. Everyday Clothing
If someone pays close attention to the aforementioned sun-protective traits and makes purchases accordingly, the right everyday clothing can be highly sun-protective: jeans, for example, have a UPF of about 1700, and you can’t do much better than that. It is also worthwhile to know that you can improve the UPF of everyday clothing. To begin with, just washing a garment a few times (especially one made from cottons or cotton blends) makes it shrink slightly, closing up holes between the fibers that let through UVR, and thereby increasing the garment’s UPF; this is especially true in Australia, where clothes are not washed before UPF testing.
Tests have shown that it is also possible to wash in extra protection with a UV-blocking additive like Rit SunGuard.6 If you have favorite garments that are not UPF-rated, washing them with certain dyes and chemical additives such as UV-cutting agents (UVCAs) can also increase the UV protection they provide.
However, for measurement and certainty purposes, UPF-rated clothing is obviously superior, since the consumer knows exactly how much protection he or she is getting. Furthermore, it is designed specifically to be more sun-protective as its raison d’etre, while everyday clothing may focus more on fashionability, sex appeal, and comfort. In any event, the latest versions of UPF clothing can also be extremely fashionable and comfortable while offering better coverage: slightly longer sleeves, light, breathable fabrics with a double layer at the shoulders (a high-UVR-exposure area), or other design factors may provide extra comfort and coolness as well as better sun protection.
Acknowledgements: Thanks to the staff of the UPF Testing Area for their assistance. Thanks also to the Cancer Council Victoria for their cooperation and assistance over the years. Images supplied courtesy of Queensland Health 2010.
- Gies P,Roy C,Javorniczky J,et al.Global solar UV index: Australian measurements, forecasts and comparison with the UK. Photochem Photobiol 2004; 79(1):32-39.
- World Health Organisation. Global solar UV index: a practical guide. Geneva, Switzerland: WHO, 2002. http://www.who.int/uv/publications/en/GlobalUVI.pdf. Last reviewed July 16, 2012.
- Standards Australia/Standards New Zealand (1996) Sun protective clothing—evaluation and classification. AS/NZS 4399, Standards Australia, Sydney and Standards New Zealand, Wellington.
- Diffey BL. Sunscreens: expectation and realization. Photodermatol, Photoimmunol Photomed 2009; 25:233-236.
- GiesP. Photoprotectionbyclothing.Photodermatol, Photoimmunol Photomed 2007; 23:264-274.
- Osterwalder U, Schlenker W, Rohwer H, et al. Facts and fiction on ultraviolet protection by clothing. Radiat Prot Dosimetry 2000; 91(1):255–259.
- CIE (International Commission on Illumination) Technical Report. UV protection and clothing, CIE 2006; 172. CIE Central Bureau, Vienna, Austria.