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I was reluctantly dragged along to do clothes shopping in Singapore today and all over the place they advertised clothing that has supposedly been coated with some form of UV protection. As far as I'm aware Singapore doesn't have the European-style of consumer protection laws where you can only claim what you can prove, which disallows statements like "Volvo is the safest car in the world."

I had my camera with me so I snapped a picture of the sign that claims the clothes UPF factor is the equivalent of SPF. I've never seen clothes like this before in my life, so I'm wondering if there's any research that show if this really is a feasible alternative to sun protection.

enter image description here

I'm of course only asking about the areas the clothing actually covers.

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With the scorching sun of Singapore (between bouts of rain) this had better work! –  Sklivvz Apr 9 '11 at 15:46
    
Speaking of rain, note that not all clothing provides as good of protection when wet (knit is usually especially bad, but a loose weave can be a problem also). So be aware--if the clothing starts to look translucent ("wet tee shirt"), UV is getting through pretty well also. –  Rex Kerr Apr 9 '11 at 17:31
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1 Answer

up vote 17 down vote accepted

Clever marketing gimmick if you live in northern climes (where I have seen this marketed), but of value in hotter climates. Basically cloth will stop/absorb UV radiation based on the weave density. No one wearing a flannel shirt will ever get burned. However, it is not practical to wear such thick clothing in the summer or hot climates. So if UV absorbent chemicals are added, it will offer additional protection without the necessary bulk. Valuable in tropical climates.

The skin cancer foundation actually does recommend this type of clothing on their site. As I said

Clothes can protect your skin against the sun's harmful ultraviolet (UV) rays. But not all clothing is created equal. The tightness of the weave, the weight, type of fiber, color and amount of skin covered all affect the amount of protection they provide.

And they even offer a couple examples

As a rule, light-colored, lightweight and loosely-woven fabrics do not offer much protection from the sun. That white T-shirt you slip on at the beach when you feel your skin burning provides only moderate protection from sunburn, with an average ultraviolet protection factor (UPF) of 7. At the other end of the spectrum, a long-sleeved dark denim shirt offers an estimated UPF of 1,700 – which amounts to a complete sun block. In general, clothing made of tightly-woven fabric best protects skin from the sun. The easiest way to test if a fabric can protect your skin is to hold it up to the light. If you can see through it, then UV radiation can penetrate it – and your skin.

Their recommendation is as expected from this

To receive The Skin Cancer Foundation's Seal of Recommendation, sun-protective fabrics must have a minimum UPF of 30. We consider a UPF rating of 30-49 to offer very good protection, and 50+ excellent protection.

The New York University School of Medicine actually did a study to back up the Skin Cancer foundation. I added emphasis on the final conclusion.

Abstract

BACKGROUND: The public has long been instructed to wear protective clothing against ultraviolet (UV) damage.

OBJECTIVE: Our purpose was to determine the UV protection factor (UPF) of two cotton fabrics used in the manufacture of summer T-shirts and to explore methods that could improve the UPF of these fabrics.

METHODS: Each of the two types of white cotton fabrics (cotton T-shirt and mercerized cotton print cloth) used in this study was divided into 4 treatment groups: (1) water-only (machine washed with water), (2) detergent-only (washed with detergent), (3) detergent-UV absorber (washed with detergent and a UV absorber), and (4) dyes (dyed fabrics). Ultraviolet transmission through the fabrics was measured with a spectrophotometer before and after laundry and dyeing treatments. Based on UV transmission through these fabrics, the UPF values were calculated.

RESULTS: Before any treatments, the mean UPFs were 4.94 for the T-shirt fabric and 3.13 for the print cloth. There was greater UVA (320-400 nm) than UVB (280-320 nm) transmission through these fabrics. After 5 washings with water alone and with detergent alone, UPF increased by 51% and 17%, respectively, for the cotton T-shirt fabric. Washing the T-shirt fabrics with detergent plus the UV-absorbing agent increased the UPF by 407% after 5 treatments. Dyeing the fabric blue or yellow increased the UPF by 544% and 212%, respectively. Similar changes in UPFs were observed for the print cloth fabric.

CONCLUSION: The two cotton fabrics used in this study offered limited protection against UV radiation as determined by spectrophotometric analysis. Laundering with detergent and water improves UPF slightly by causing fabric shrinkage. Dyeing fabrics or adding a UV-absorbing agent during laundering substantially reduces UV transmission and increases UPF. More UVA is transmitted through the fabrics than UVB.

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Before researching this, I actually thought it was a complete marketing gimmick with no validity. Learn something new every day! –  Larian LeQuella Apr 9 '11 at 17:08
    
I wonder by what mechanism simply laundering a fabric in water might increase the UPF. –  Oddthinking Jun 7 '11 at 13:01
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