What is Ultraviolet Protection Factor (UPF)?
Unlike SPF (Sun Protection Factor) that traditionally uses human sunburn testing in a laboratory environment, UPF measures both UV radiation transmittance using a laboratory instrument (spectroradiometer) and an artificial light source and translates these results using a mathematical expression based upon the sunburn action spectrum (erythema action spectrum) integrated over the relevant UV spectrum. Theroretically, both human SPF testing and in vitro laboratory instrument testing measure a product’s relative ability to protect against minimal sunburn compared to skin that is not protected.
Sun protective clothing and textile/fabric manufacturers are currently a self-regulating industry in North America, prescribed by the AATCC and ASTM methods of testing.
UPF Ratings and Protection Categories
|UPF Rating||Protection Category||% UV radiation Blocked|
|UPF 15 – 24||Good||93.3 – 95.9|
|UPF 25 – 39||Very Good||96.0 – 97.4|
|UPF 40 – 50+||Excellent||97.5 – 99+|
All fabrics disrupt UV radiation to some degree. When ultraviolet radiation and textiles interact, the energy of UV rays is changed. UV radiation is converted to heat, a transformation that renders most rays harmless. Some garments, depending on factors such as construction, dyes and fabric treatments, do a better job at this than others. A white cotton t-shirt offers an ultraviolet protection factor (UPF) of five. Clothing that is thicker, more tightly knit and darker in color has a higher UPF rating.
- Construction: Dense, tight construction (either weaves or knits) minimizes the spaces between yarns, which in turn minimizes the amount of UV light that can pass through. Some tightly constructed UPF-rated garments use vents to boost air circulation and help the wearer stay cool. Thicker fabrics also help reduce UV transmission.
- Dyes: It is the specific type of dye (and the concentration in which it is used) that impacts a fabric’s UV transmission, not its color. Some dyes deflect more UV radiation than others, and some absorb none at all—including black dyes. How can one know what kind of dyes are used in individual garments? The only tip-off is if the garment carries a UPF rating. Clothing engineered for UV protection may use high concentrations of premium dyes that disrupt UV light. Such dyes include “conjugated” molecules that disrupt UV radiation. The higher the concentration of such dyes, the darker the garment becomes. But ultimately color has no influence on UV rays. Note: Pigment-dyed fabrics, which include a resin that creates a powdery look and feel, get high marks for UV protection.
- Treatments: Chemicals effective at absorbing UV light may be added during processing. Specialized laundry additives, which include optical brightening agents and newly developed UV-disrupting compounds, can boost a garment’s UPF rating.
- Fiber type: Polyester does an excellent job at disrupting UV light (due to hydrogen- and carbon-based benzene rings within the polymer). Nylon is good. Wool and silk are moderately effective. Cotton, rayon, flax and hemp fabrics (natural fibers composed of cellulose polymers) often score low without added treatments. However, unbleached or naturally colored cotton performs better at interacting with UV light than bleached cotton.
- Stretch: If a garment is stretched 10% or more beyond its normal dimensions, spaces between yarns are widened and its effectiveness against UV light may be reduced up to 40%.
- Wetness: A fabric’s ability to disrupt UV radiation is usually reduced when wet, though the reasons why are not completely understood. Wetness may cause a 30% to 50% reduction in a fabric’s UPF rating.
- Condition: Worn or faded fabrics are less effective against UV light.
Optical Brightening Agents (OBAs), fabric whitening agent or Fluorescent Whitening Agents (FWA) are fluorescent dyes that glow blue-white when exposed to ultraviolet light. The blue-white colour makes yellowed fabrics appear white. Most common household detergents also include OBAs, so repeated launderings will increase the fabric’s accumulation of brighteners and thus increase its UV-protection by disruption of UV radiation.
FWA-1 has the chemical name Disodium 4,4′-Bis[(4-Anilino-6-Morpholino-1,3,5-Triazin-2-Yl)Amino]Stilbene-2,2′-Disulphonate and the following chemical structure:
FWA-5 has the chemical name Benzenesulfonic acid, 2,2’-([1,1’-biphenyl]-4,4’-diyldi-2,1-ethenediyl)bis-, disodium salt.
A study paper on the effects of repeated laundering of UPF-rated clothing was published in November, 1998, in Textile Chemist and Colorist, an industry journal.
The paper’s conclusions assert that “repeated home launderings (regardless of whether or not the detergent contains an OBA [optical brightening agent, the compound commonly found in household detergents, mainly to “keep whites white”]) does not reduce the UPF rating of a woven or knitted fabric of cotton, polyester, or nylon. On the contrary UPF ratings are enhanced or remain unchanged by repeated launderings up to 20 times.”
SunGuard works by penetrating the fibers of washable clothing and coating them with a formula that blocks ultraviolet rays. The active ingredient is Tinosorb FD that was developed by Ciba Labs, based in Switzerland. Listed product ingredients:
Ciba Tinosorb FD
SunGuard is safe for all washable natural fabrics including cotton, linen, rayon and silk. It will not add sun protection to polyester, acrylic or other synthetic fibers. It can be used on blended fabrics but the final protection will not be as effective. To use, one package of SunGuard is suitable for small to large loads. Select the hottest water suitable for each type of fabric. Add SunGuard as the washer is filling with water. Add the clothing and be sure not to crowd the washer or overload. It is best if the wash cycle is at least 15 minutes – this can be agitation or soaking time. After fifteen minutes, rinse and dry as usual. Detergent, bleach or other additives should not be added during the initial treatment.
After the initial treatment, the sun protection factor will last through twenty washings. You may use bleach, stain removers and detergent as usual. They will not affect the SunGuard protection formula. It is recommended for use on children’s clothing after the age of six months. It cannot be used as a spray-on treatment for hats, umbrellas or outdoor fabrics.
SunGuard has received the Skin Cancer Foundation’s Seal of Recommendation and the Good Housekeeping Seal of Approval.
“You might get fine UV protection from a regular piece of clothing,” says Dr. Martin A. Weinstock, professor of Dermatology and Community Health at Brown University Medical School and the chairman of the Skin Cancer Advisory Group of the American Cancer Society. “But with UPF-rated clothing, you’re assuring that protection.”