Sun protection with textiles, keeping cool head on hot days
In summer, sun protection is literally a hot topic. Shading textiles such as sunshades, blinds and beach shelters promise to provide cooling shade and protection from harmful UV radiation. There is also more and more specific UV protection clothing to be found in the shops.
But how in fact do textiles protect you from the sun's radiation, and what differences between them should be taken into account? Dr. Andreas Schmidt of the international Textile Research Centre at the Hohenstein Institute in Bönnigheim has the facts:
Why do special UV protection textiles provide even better protection from the sun than cosmetic sun blockers with a high sun protection factor (SPF)?
The sun protection is, as it were, built into the processed chemical fibres. Titanium dioxide particles, such as are found in powders and sunscreen, are incorporated into the fibres and act like tiny mirrors there, reflecting the high-energy UV rays and so protecting the skin beneath.
In addition, the UV protection in sun protection textiles is increased still further by special ways of constructing the fabrics, for example laying several layers on top of one another, covering the gaps between the fibres that inevitably occur in woven or knitted fabrics.
Which criteria determine the UV protection factor of textiles?
As well as the composition of the material, the way it is put together and the weight, the colour and surface finish of the materials also have an important effect on the UV protection factor (UPF) of a textile material.
What role does the colour of a textile material play in the UV protection factor?
Dark colours generally give better UV protection than pale colours, because the dye pigments also absorb UV radiation. This is why the Tuareg people in the Sahara have been dyeing their clothing dark blue for centuries. However, thanks to chemical treatments like UV absorbers, it is also possible nowadays to achieve similar results with lighter coloured fabrics.
Why do natural fibres only offer limited protection from UV radiation?
The UV protection given by natural fibres such as cotton or linen is relatively low. A white Tshirt has a UV protection factor of 10-15. The reason for this is that cotton fibres in themselves reflect or absorb little UV radiation. This is particularly true once they have
become wet - the fibres then become almost see-through.
Without this effect, there would be no such thing as wet T-shirt contests, for example (he laughs)! In addition, cotton fibres are kidney-shaped in diameter, i.e. within one fibre the diameter can be very variable. When this is combined with a twisted fibre structure, quite large holes appear in woven or knitted fabrics, through which the UV radiation can penetrate unhindered to the skin below.
Are there any natural fibres with a good UV protection factor?
Natural silk has a relatively high UV protection factor, because, like modern synthetic fibres, it contains matting components which reflect and absorb UV rays. The regular fibre structure, with small gaps in woven or knitted fabrics, also prevents the UV radiation from reaching the skin. Depending on the colour, the UPF may be 20 to 30. There is a good reason why in India, for example, silk sarongs are worn wrapped in several layers, which significantly increases the UV protection factor.