Does clothing offer good UVR protection?
Most sun protective garments rely on the fabric's natural ability to block UVR. Sun protective garments are not usually specially treated, although chemical treatments are available. Laboratory testing determines how effective a material is at blocking UVR and this is often stated on the garment label as a UPF rating. The UPF rating of a material can be determined by placing it under a UVR lamp and measuring the amount of UVR that passes through the fabric. From this UVR transmission data the UPF rating can be calculated.
The UPF rating indicates how much the material reduces UVR exposure. For example, a material with a UPF rating of 20 would only allow 1/20th of the hazardous UVR falling on its surface to pass through it. A garment made from this material would reduce UVR exposure on the areas of skin it covered by a factor of 20.
The UVR protection offered by different types of fabrics varies considerably and depends on the factors listed below.
What makes a good sun protective garment?
Several factors determine how effective garments are at reducing UVR:
- Composition of the fabric: Different materials such as cotton, polyester and nylon have different natural UVR-absorbing properties.
- Weave density: Less UVR passes through tightly woven or knitted fabrics. As shown below the smaller the spacing between the individual fibre strands the higher the protection.
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- Colour: Many dyes absorb UVR. In darker colours of the same fabric type (black, navy, dark red) will absorb UVR more strongly than light pastel shades (white, sky blue, light green) and consequently will have a higher UPF rating.
- Tension: Stretching a fabric may cause a decrease in the UPF rating. This is common in knitted or elasticised fabrics and care should be taken to select the correct size for the wearer.
- Weight: Heavier weight materials generally have a higher UPF ratings than lighter materials of the same type.
- Moisture content: Many fabrics have lower UPF ratings when wet. The drop in UPF rating depends on the type of fabric and the amount of moisture it absorbs when wet.
- Design: As well as considerations of fashion and comfort, selecting garments that are sensibly designed for sun protection can make a large difference to your overall UVR exposure. A shirt with long sleeves and a high collar offers more protection than a short-sleeve shirt without a collar. Loose fitting garments give better protection than garments that are worn close to the skin and also may be more comfortable to wear on hot days. A legionnaire style cap with a flap protects the ears and back of the neck. A broad-brimmed hat shades the face and neck.
- Condition: Unless otherwise stated, UPF ratings are made on fabrics that are in new condition. The UPF rating of many cotton based fabrics can improve over the "new" rating after they have been washed at least once. Shrinkage in these fabrics closes small gaps between the fibres and allows less UVR to pass through. However, old, threadbare or faded garments may have a lower UPF rating.
- UVR absorbers: Some fabrics are treated to improve the UPF rating. This is usually done if the base fabric has a low natural resistance to UVR. Treatment with a UVR absorber, generally during manufacture, can result in a fabric with a higher UPF rating that still retains the comfort properties of the original fabric. Many dyes absorb UVR and therefore increase the UPF rating of the fabric. Some UVR absorbers behave like colourless dyes. They bond to the fabric in a similar way, and have a comparable permanency to coloured dyes. Recently there has been interest in adding UVR absorbers to commercial washing powders.
| Page created 19th November 2003 |
URL:www.arpansa.gov.au/uvrg/rginfo_p9.html |
Last updated 24th November 2003 |
