How to Increase the UPF of a T-shirt
Diana Clarke
Whatever style you wear this summer, you want it to be comfortable. And what is more cool and enduring than a cotton T-shirt you can accessorize to your heart’s content. You may already have several T-shirts you cherish. But have you thought about the shirt’s UPF? That stands for Ultraviolet Protection Factor, the standard rating system that tests and measures a fabric’s ability to protect the skin from the initial onset of skin reddening caused by UV-B rays.
UPF values
15 to 24 good sunburn protection
25 to 39 very good sunburn protection
40 to 50 excellent sunburn protection
A new white cotton t-shirt has a UPF of about 5. So that means about 1/5 of UV rays are transmitted through to your skin. Wash the t-shirt once and it shrinks, decreasing the spaces between the fibers in the fabric. This tightening of the weave increases UV protection by increasing the cover factor, the surface area of the fabric covered by fibers.
“Cover factor is the MOST important factor in achieving UPF ratings of at least 15 UPF, the lowest value for classifying a fabric as Ultraviolet protective,” says Kathryn Hatch, Ph.D., professor, Agricultural and Biosystems Engineering, University of Arizona, Tucson, AZ.
That’s about 1/15 of UV Rays getting through to your skin. However, UV radiation can also penetrate some fabrics, allowing UV rays to be transmitted. In addition, “Skin that is not covered is NOT protected. Garments styled to cover the most skin are better for sun protection,” says Dr. Hatch.
You can also wash the t-shirt several times in most laundry detergent which will deposit optical whiteners on the cotton fibers. “The more washings a fabric undergoes, the higher the chemical build-up,” says Dr. Hatch.
To achieve broad spectrum UVA/UVB protection, you can add a UV absorbing compound to your laundry detergent during washing. Rit SunGuard, recommended by the Skin Cancer Foundation, can increase the UPF of a T-shirt from 5 to 30 after a single washing and will last for 20 washes.
“The big difference between SunGuard and optical whiteners is that SunGuard is much more effective in absorbing the most skin reddening UV rays,” says Dr. Hatch.
If the shirt contains a blend of cotton and polyester, the UPF will increase because polyester absorbs UV rays better than cotton, says Dr. Hatch. However, optical whiteners will not deposit on polyester. And optical whiteners do not absorb UV-A rays.
Dyes and pigments can also contribute to the UPF rating, but a consumer cannot judge a shirt’s UPF by its color because different dye types, concentrations and sometimes combinations of dyes are used in a fabric.
“A consumer knows the fabric type by the label but not the dyes that were used in creating the garment,” says Dr. Hatch.
On the other hand, stretching cotton jersey, for example, both vertically and horizontally, can decrease the UPF with the exception of horizontal stretching alone, which will help bring the fibers or yarn closer together. Also, wear and tear, or letting a t-shirt get wet, will decrease the UPF, says Dr. Hatch.
There is one misconception worth mentioning. Holding fabric up to the light to determine if UV radiation is getting through is not reliable. “You can’t use visual perception, which sees only visible light, not the UV light that may be transmitted,” says Michael Martin, M. D., MPH, who is on the faculty at UCSF and sees patients at San Francisco General Hospital.
Dr. Martin, who wrote How to Outsmart the Sun in 1993, has been practicing sun protection for more than 15 years. He recommends a 3-step approach to sun protection.
1. wear a broad spectrum sunscreen that protects against UVA and UVB radiation because most people don’t cover up all their skin, particularly their face and hands.
2. cover up as much of the body as possible and wear a wide- brimmed hat and sunglasses that block out UV rays. And seek shade under a parasol or canopy to shield yourself from the sun.
3. avoid the sun, particularly at midday when sunlight is the most intense.
“This three-step approach is very effective and beneficial in the vast majority of cases. Each factor backs up the other,” says Dr. Martin. “You can’t say sunscreen is all you need, avoiding the sun is all you need, or clothing is all you need.”
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Last modified: 06/22/07
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