When I began to design my shirts for this first collection, I really wasn't thinking... it's gotta be a "sun shirt"! My real goal was a great fitting shirt, with a polo collar, that I could lesson in, get sweaty, stay cool, feel comfortable, etc. As I moved along in the design process, I added in fun colors and cool prints (why be conservative the first go round?) I've had several people refer to them as "sun shirts" and many tack shops ask about their sun protective properties. So... I needed to get into it, and I ended up with a lot of research. I'll go over the main points here.
I'll start with SPF vs UPF. Both SPF (Sun Protection Factor) and UPF (Ultraviolet Protection Factor) are standards used to measure protection from the sun. SPF is the standard used to measure the effectiveness of sunscreens and is only used to rate a sunscreen’s ability to protect against UVB rays (unless specifically Broad Spectrum SPF is indicated.) UPF is the standard used to measure the effectiveness of sun protective fabrics and indicates how much of the sun’s UV radiation penetrates a fabric and reaches the skin.
You will see a UPF rating from 15-50 associated with products that claim they are sun protective. A fabric with a rating of 50 will allow only 1/50th of the sun’s UV rays to pass through. This means the fabric will reduce your skin’s UV radiation exposure significantly because only 2 percent of the UV rays will get through. This also means that it blocks both UVA and UVB rays. Currently, in the United States, the standards for UPF are voluntary and fabrics must be independently tested for ratings.
There are other factors that change a textile's UPF rating over time... if the fabric was treated with a chemical to increase its UPF, that chemical will lose effectiveness after repeated washes (only testing can determine how many washes.) Dyes added to the fabric can increase the UPF (depending on how those dyes break down, it can then lose UPF.) Repeated washing of certain fibers can increase the UPF as they shrink and the weave becomes denser. Repeated stretching can decrease UPF, making the weave of the fibers looser. The list goes on and on and UPF goes up and down.
As I began sourcing for textiles, I specifically rejected any textile that had been coated with an unnatural chemical. I was really hoping to be eco-friendly. There are many textiles that are pre-tested and claim a UPF rating, usually because they have been pre-treated with something. I ended up with two white fabrics and a plan to add prints via sublimation printing. As I started to show the shirts, the questions about sun protection came in and the shirts seemed to be automatically lumped into the "sun shirt" category.
Independent lab testing was the only thing I could do to ethically answer any questions about the fabric's sun protection ability. While I never made any claims about the shirts, I could only address the situation if I knew for certain. I sent the fabrics out for testing and waited.
Great news! Both fabrics came back with the ability to protect us from the sun! The main fabric (used for the front, collar, cuffs and the top of the arms) came back with a rating of 50+ and sits high in the Excellent category. The secondary fabric (used for the side panels and back) came back with a rating of 15 and falls nicely in the Good category. (While I was dismayed at the fact that both fabrics weren't overachievers, the lab tester assured me that the Good rating is still a success, and was tested at blocking 91.71% of UVA and 96.38% of UVB. As a comparison, my main fabric that was rated at UPF50+ blocks 97.27% UVA and 98.67% UVB. So Good isn't too far behind.)