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Clothing is a great way to protect your skin, but not all clothing protects equally. Find out which fabrics and colors offer the greatest protection.

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.

What a UPF Rating Really Means

UPF stands for Ultraviolet Protection Factor and indicates how much of the sun's UV radiation is absorbed. A fabric with a rating of 50 will allow only 1/50th of the sun's UV rays to pass through. This means the fabric will reduce your skin's UV radiation exposure significantly, because only 2 percent of the UV rays will get through.

What's the Difference between UPF and SPF?

SPF stands for Sun Protection Factor and is the rating you're familiar with for sunscreens and other sun-protective products. It measures the amount of time it takes for sun-exposed skin to redden, while UPF measures the amount of UV radiation that penetrates a fabric and reaches the skin.

Which Fabrics Are Best?

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.

The color of the fabric also plays a role. Darker-colored fabrics are more effective than lighter at blocking out the sun. For instance, the UPF of a green cotton T-shirt is 10 versus 7 for white cotton, and a thicker fabric such as velvet in black, blue or dark green has an approximate UPF of 50.

Fabric Content and the Wearer's Activity Make a Difference

What the clothing is made of matters. Fabrics such as unbleached cotton contain special pigments called lignins that act as UV absorbers. High-luster polyesters and even thin, satiny silk can be highly protective because they reflect radiation.

Even if the piece of clothing has a good UPF, what you do while wearing it can make a difference. If the fabric gets stretched, it will lose some of its protective ability, because the fabric becomes thinner and more transparent to light. And once it gets wet, it can lose up to 50 percent of its UPF. In Florida, it is a common practice for parents to put a white T-shirt on their children to protect them from the sun while swimming. But when that T-shirt gets wet, it provides a UPF of only 3.

Consider High-Tech Clothing

When selecting clothes for sun protection, consider fabrics that have been specially treated with chemical UV absorbers, known as colorless dyes. These prevent some penetration of both UVB and UVA rays. A number of manufacturers are now making special sun-protective clothing that has been treated with a chemical sunblock during the manufacturing process. In addition, they use fabrics of the weave and colors that provide protection best. The garments are designed to cover as much of the skin as possible.

New standards for sun-protective fabrics in the US were unveiled in January, 2001. UPF is similar to SPF, in that they both measure protection.

Only clothes with a UPF of 15-50+ may be labeled as sun-protective. Clothes that are marketed with a sun-protective claim are usually UPF 50+. Also, like regular clothing, sun-protective clothing may lose its effectiveness if pulled too tight or stretched out, if it becomes damp or wet, or if it is washed and worn repeatedly.

Wash Sun Protection Into your Clothes

A laundry additive, Sun Guard, contains the sunscreen Tinosorb. When added to a detergent, it increases the UPF of the clothing, and this protection lasts through 20 washings.

The Foundation's Recommendation

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.