Fabrics and clothing for protection against the sun

Also see Sun Protection Products for a list of companies selling fabrics and clothing.

When choosing clothing for sun protection, you want clothing to cover up as much skin as possible; thus high or turned up collars, long sleeves and long pants or skirts are a good choice.  Next, you want fabrics to block or reflect as much light as possible. In general, heavier, tightly woven, dark fabrics protect better than light, loose, light fabrics. Finally, there are a couple different ways of measuring fabric sun protection:

• SPF: the old fashioned Sun Protective Factor (SPF) rating which measures only UVB radiation and is used on sunscreens, 
• UPF, and the new ultraviolet protection factor-UPF rating which  measures both UVB and UVA radiation blocked. (See Sunscreens for a description of UVA and UVB light.)

Common sense home fabric test:

A useful rule of thumb is to hold a shirt up to a strong light source such as a light bulb. If you can see images through it, it probably has an SPF value less than 15. If light gets through, but you can't really see through it, it probably has a SPF value somewhere between 15 and 50. If it completely blocks all light, it probably has an SPF value greater than 50 (e.g. heavy cotton denim).

SPF ratings of fabrics and clothing (Sun Protection Factor)

Clothing is generally a good UV blocker, although lighter fabrics that are desirable because they are cooler may not have as great a protective value as heavier fabrics such as denim, which is generally the most protective. The sun protection value of fabric is more a function of the hole size of the fabric mesh than the particular fabric type Typical summer shirt fabrics only have an SPF of 6.5. Some articles say that denim has an SPF value of 50 or more. Darker color fabrics provide greater protection from UV rays than do lighter color fabrics.  

Figure 1: Tight weave of fabric blocks sun resulting in greater protection and higher UPF and SPF

Finally, fabric type should be considered.  Bleached cotton has an SPF of 7 or 8. Cotton and polyester/cotton blends offer comparable protection. When stretched, Lycra fabric is significantly less effective than when it is lax.  It is also important to note that fabrics are significantly less photo-protective when wet. One study examined the SPF of various fabrics and found that polyester offered more protection than cotton, wool, rayon, nylon and linen1. [Sun Protection and Sunscreens] The SPF values for white fabrics is listed in Table 1.

Table 1: SPF values for variousfabrics:

Protecting against UV light in clothing or UPF: ultraviolet (UV) protection factor 

A new standard that measures UV light is called the ultraviolet protection factor (UPF). The UPF rating indicates how much the material reduces UVR exposure. For example, a material with a UPF rating of 20 would only allow 1/20th of the hazardous UVR falling on its surface to pass through it. You can judge how well a UPF fabric protects by the guidelines listed in Table 2.

Table 2:  Evaluating UPF Protection

UPF Fabric Value	Category
At least 15 to 24	Good UV Protection
25 to 39	Very Good UV Protection
+40 or higher	Excellent UV Protection

Think about the following factors when choosing clothing and fabrics to improve protection against UV light.

• Fabric type: Wool, polyester are better  than cotton and linen. Heavier weight materials are better than light materials.
• Tight weave:: Less UVR passes through tightly woven or knitted fabrics.  Stretching fabrics makes holes bigger, so get the right size clothing.
• Color: Darker colors (black, navy, dark red) will absorb UVR better than light colors.
• Dry fabrics are better than wet fabrics. (think wet T-shirt contests.)
• Clothing design that covers up more skin is better than design that doesn't. A shirt with long sleeves and a high collar offers more protection than a short-sleeve shirt without a collar. Loose fitting garments give better protection than garments that are worn close to the skin and also may be more comfortable to wear on hot days. [http://www.arpansa.gov.au/uvrg/rginfo_p9.html]

In a study of 236 typical summer fabrics, they found the following:  Polyester and wool fabrics usually provide sufficient UV protection (UPF 30+), while other fabrics, such as cotton, linen, and viscose, frequently offer poor UV protection. We showed that dark-coloured fabrics frequently have UPF values of 30+. Nevertheless, also white fabrics may provide sufficient UV protection depending on other parameters such as tightness of weave and fibre type. The most striking result however is the fact that 78 fabrics (33%) have an insufficient UPF of less than 15, and only 113 fabrics (48%) fulfilled the requirements of the European standard for UV protective clothing, that is UPF 30+ [4]. [http://www.biomedcentral.com/content/pdf/1471-5945-1-6.pdf  ]

Special fabrics and products made for UV protection

Some fabrics are specifically made for UV protection  and can have an SPF of around 30.  Solumbra is the fabric used by Sun Precautions. It is a light weight, synthetic type  material. It is specifically designed to protect against the sun and UV rays.

UVR absorbers: Some fabrics are treated to improve the UPF rating. This is usually done if the base fabric has a low natural resistance to UVR. Treatment with a UVR absorber, generally during manufacture, can result in a fabric with a higher UPF rating that still retains the comfort properties of the original fabric. Many dyes absorb UVR and therefore increase the UPF rating of the fabric. Some UVR absorbers behave like colourless dyes. They bond to the fabric in a similar way, and have a comparable permanency to coloured dyes. Recently there has been interest in adding UVR absorbers to commercial washing powders.[http://www.arpansa.gov.au/uvrg/rginfo_p9.html]

Solarveil
Solarveil is manufactured using complex yarn structures and a complex knitting procedure. This construction of Solarveil causes the UVA and UVB rays to be reflected (bounced off) and refracted (bent and scattered) preventing most of them from penetrating Solarveil . Additionally, Solarveil is treated with proprietary UV inhibitors that absorb UV rays, further preventing the rays from penetrating the fabric. A single layer of Solarveil blocks an average of 75% of both UVA and UVB rays with a high of 80%. A double layer blocks from 92% to 95%. Most of the Solarveil styles are made with a double layer 
http://www.solarveil.com/technical.asp 

Laundry  additive to increase protection of clothing

Rit, the dye brand, has created colorless sunscreen you wash into clothes. 
SunGuard works by washing an invisible shield into clothing that helps block more than 96% of the sun's harmful rays from reaching your skin. With the active ingredient TINOSORB® FD, a UV protectant from Ciba Specialty Chemicals, SunGuard can boost the UPF protection of a white cotton T-shirt from UPF 5 to UPF 30.

And, SunGuard is so easy to use! Add one package of SunGuard to a warm or hot water laundry load along with laundry detergent and you wash in skin protection for up to 20 washings. SunGuard won't change the color or comfort of clothing and is safe for even the most sensitive skin.
http://www.sunguardsunprotection.com        

References

Protection against ultraviolet radiation by commercial summer clothing: need for standardised testing and labelling
Thilo Gambichler , Sebastian Rotterdam , Peter Altmeyer and Klaus Hoffmann, Department of Dermatology, Ruhr-University Bochum, Bochum, Germany, BMC Dermatology 2001, 1:6, 5 October 2001[http://www.biomedcentral.com/content/pdf/1471-5945-1-6.pdf  ]

Resource Guide for UVR Protective Products UV Reference [http://www.arpansa.gov.au/uvrg/rginfo_p9.html]

http://www.cancer.org/docroot/SPC/content/SPC_1_Sun_Protection_Ratings_For_Summer_Clothes_and_Fabrics.asp

AMERICAN STANDARDS FOR UV-PROTECTIVE TEXTILES
Kathryn L. Hatch, The University of Arizona, Tucson AZ 85721 [www.extension.iastate.edu/textiles/pdf_files/Hatchs_Insert.pdf] 

[ Menter] Clothing as solar radiation protection., Menter JM, Hatch KL., Curr Probl Dermatol. 2003;31:50-63.