When it comes to offering protection from the sun, not all clothing is created equal.

If you've ever gotten a sunburn right through the long-sleeved T-shirt you were wearing, you already know this. But what allowed it to happen?Chances are your shirt was made from a summer-weight fabric with a sun protection factor of a measly 7 or 8 - well below the minimum SPF 15 recommended by dermatologists. Get the shirt wet and the SPF number can drop to 5 or 6.

"You can't just put on any shirt and expect it to protect you," says Julian Menter, research professor of medicine at Morehouse School of Medicine in Atlanta. "Fabrics can differ greatly in their ability to shield you from ultraviolet radiation."

At the high end of the protection scale is Solumbra, a relatively new, tightly woven, synthetic fabric credited with an SPF of 30. Light enough for warm-weather wear, Solumbra is machine washable and described as being "soft as brushed cotton."

Menter tested Solumbra against the same sort of woven cotton found in work shirts and discovered that while the latter protected laboratory mice against short-term UV effects, it did not shield them from long-term skin damage such as skin cancer. In fact, the incidence of tumors was comparable to that of the mice that received no protection.

Mice that were either not subjected to UV radiation or that were protected by Solumbra fabric showed no signs of skin damage, according to an article that appeared in FDA Consumer, the magazine of the U.S. Food and Drug Administration. (Clothing that is labeled or promoted as providing protecting against the sun or limiting exposure to UV rays is considered a medical device by the FDA.)

Solumbra is available in a line of clothing and accessories made by Sun Precautions, a Seattle company founded by Shaun Hughes. When Hughes was 26, a malignant melanoma was removed from his shoulder and he resorted to wearing sunscreen and paper towels under his clothes as precautions against recurring cancers.

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Nearly 14 years later, Hughes has most likely thrown in the towels. The Sun Precautions catalog is filled with pictures of protective clothing that ranges from button-front shirts (about $80) and tailored pants ($75) for men to leggings ($63) and a calf-length skirt ($70) for women. Most items are available in sizes XS to XL. Larger sizes are available only in selected items, such as the man's safari shirt and unisex pants.

Clothing for children includes colorful polo shirts ($35) and coveralls for toddlers ($45). Wide-brimmed hats are available in Solumbra or good ol' straw ($46 to $50).

For information or to request a catalog, call 1-800-882-7860. Some items of Solumbra clothing are also available at cancer centers.