What the Heck Are Sun Safe Clothes?

In an earlier post, I talked about the exponential increase in skin damage risk with decreasing as wavelength. For example, radiation at 280 nm might cause about 1000 times more damage than radiation at 340 nm. Luckily, the stratospheric ozone layer absorbs radiation with wavelengths between 100 nm and 290 nm, which is the UVC and a fraction of the UVB radiation. However, what about the rest of the UVB and the UVA part of the solar spectrum? When you are a regular reader of my blog you know that I am a huge fan of sun protective clothing. Read to learn what are sun safe clothes and how they can protect you from the harmful UVB and UVA radiation.

Disclosure: This educational post is sponsored by Coolibar. They did not endorse this post. I wrote it entirely myself using my expertise as an atmospheric scientist and the resources listed in the references.

How to Rate UV Protection?

The international scientific community has established the Ultraviolet Protection Factor (UPF) to rate the UV protection of sunscreens, fabrics or colored glasses. The Coolibar skirt in the outfit photo, for instance, is rated UPF 50+. This means that only 1/50th of the UV radiation falling on the skirt pass thru it and blocks 49/50th, i.e. 98% of the UV radiation. Science suggests UPF rating of 40+ or 50+ as being “totally” safe “sun-blocks”.

Or explained in a non-scientific way: If normal fair skin person exposed continuously to UV radiation would start reddening (erythema) after 10 minutes without sun shield, using a UPF15 sun shield would delay the time of onset of reddening to 150 minutes. This means the person could stay 15 times longer in the sun before reddening would occur.

Why Are Some Fabrics Sun Protective and Others Aren’t?

The UPF of a finished garment depends fabric porosity, type, color, weight and thickness. Application of UV absorbers like sun-bouncing minerals, titanium dioxide and zinc oxide into the yarns or onto the textile surface can increase the UPF of fabrics significantly.

Factors that might alter a fabric’s effectiveness of UV-protection are stretch and wetness.

In plain English, the fabric fails to cover the skin and/or absorb UV radiation.

Fabric Characteristics Determining the Cover Factor

Typically, weight dominates the effects of different knitted fabric structures on UPF. The definition of the cover factor is the fraction of surface covered by yarns. It corresponds to the quotient of area covered by yarns and total area of web and varies between 0 and 1. Consequently, multiplication with 100 gives the cover factor in percent.

Course density gives the number of visible loops per unit length counted along a wale. On the contrary, wale density indicates the number of visible loops per unit length counted along a course. Stitch density is the product of course density times wale density. Thus, stitch density gives the change of courses and wales per unit area. Why is this important for sun protection?

What Is the Impact of the Knit Technic on UPF

The UPF value is 100/porosity. Porosity, among other things, depends on stitch density. In knits, machine gauge, yarn parameters like yarn count, and the nature of knitting structure affect the stitch density. Typically, pore size decreases with increasing stitch density, which depends on the knit pattern. Let’s compare, for example, a knit-and-miss pattern with a knit-and-tuck pattern. The miss loops pull the knitted loops close together thereby increasing the stitch density. At the left side of the knit, the missed loops contribute to hinder UV radiation from penetrating thru the knit. This means that the miss-and-knit pattern yields a higher UPF value than a knit-and-tuck pattern.

Mean UPF increases with mean increasing stitch density in single knitted fabrics except for plain and pineapple pattern.

What Happens When UV Radiation hits a Fabric?

Theoretically, fabric can transmit, absorb or reflect as shown in the next figure. Some fibers tend to absorb a fraction of the UV radiation and convert it into heat. Another fraction is reflected in all directions, while in case of non-sun safe fabrics, the fabric transmits some fraction of the UV radiation to your skin. The latter means that a fraction of the UV radiation penetrates directly thru interstices between the fibers and yarns of the fabrics. In turn, your risk of skin cancer may increase according to the Skin Cancer Foundation.

How Do Wear and Tear Influence Mean UFP?

Shrinking of fabrics after washing reduces the space between intersectives and consequently increases the UPF. As aforementioned, usage of UV absorber increases the UPF value. Luckily, sweat, chlorine, salt and multiple laundering do not impair them when these UV absorbers were infused at the fiber level.

The natural color pigments and waxes of natural fibers absorb UV radiation. Thus, naturally colored cotton can absorb more UV radiation than bleached or dyed cotton. Stretching decreases the cover factor and UFP because it increases the pore size.

What Does this Mean for You?

As explained above, what are sun safe clothes depends on a very complex relationship between fabric weight, stitch density, knit or weave patterns, yarn treatment and type as well as color. When buying clothing, you don’t know many of these factors like absorption by color, yarn treatment or stitch density. Therefore, you best bet and safest way to ensure that you buy sun protective clothing is to look for pieces marked to have 50+ UFP. Look for items with the Coolibar Shield for up to 90% skin coverage. To not self-sabotage your skin, make sure you check the size chart so the clothes fit well. Recall, too tight means stretching and a decrease in protection.

Where to Find Stylish, Affordable Sun Protective Clothing?

Coolibar offers stylish and timeless collections of sun protective clothing for women, men and children for work and play. All their pieces are very affordable, well-made and high quality and can be easily coordinated with each other. Browse their collections now.

Do you know that you can get a sunburn in the shade when not wearing sun safe clothes and using appropriate sun cream?

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References

Allen, M.W. and Bain, G. (2018) Measuring the UV Protection Factor of Fabrics, Thermo Fisher Scientific, Madison, WI, USA. Measurement Standards Laboratory of New Zealand, Ultraviolet protection rating of fabrics.

Gambichler T., Altmeyer P., Hoffmann K. (2002) Role of Clothes in Sun Protection. In: Dummer R., Nestle F.O., Burg G. (eds) Cancers of the Skin. Recent Results in Cancer Research, 160. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-59410-6_3

Kan, C.W. (2014) A Study on Ultraviolet Protection of 100% Cotton Knitted Fabric: Effect of Fabric Parameters. The Scientific World Journal, 2014, Article ID 506049, 10 pages, https://dx.doi.org/10.1155/2014/506049

Singh, M.K., Sigh, A. (2013) Ultraviolet Protection by Fabric Engineering, Journal of Textiles, 2013, Article ID 579129, 6 pages, https://dx.doi.org/10.1155/2013/579129

Stankovic, S.B., Popovic, D., Poparic, G.B. and Bizjak, M. (2009) Ultraviolet Protection Factor of Gray-state Plain Cotton Knitted Fabrics. Textile Research Journal, 79, 1034–1042

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