We tested five cool, comfortable boating shirts to find out just how effective UPF ratings are in predicting ultraviolet light penetration.
UVA, UVB and UPF
UVA and UVB light are two wavelengths of ultraviolet light (long and short, respectively) responsible for sunburn, skin damage and eventually skin cancer. UV protection factor (UPF) is a measure of how much UV light is blocked. Ratings of 15 UPF or higher afford good protection. UPF ratings of 50 may be better, but in truth, the higher the UPF factor, the smaller the added benefit.
For instance, you might think UPF 30 is twice as good as UPF 15, but in truth UPF 30 only blocks up to 1.5 percent more UV light than UPF 15. A UPF 50 only blocks up to 3.1 percent more than 15. The trade-off can be a less comfortable, less breathable garment. Why? Because the tighter the weave, the higher the UPF rating. Darker colors also block more UV light but convert it into heat within the fabric. But that’s where a garment’s design comes in.
To illustrate this we took micro photos of the fabrics to show weaves and then backlit them with UV light to show penetration.
Blocking the Sun
Wearing a tightly woven nylon shirt could feel like wearing plastic wrap if it weren’t for wicking fibers, mesh linings and air vents. Tightly woven cotton is a good UV blocker and often feels cooler than synthetics until it gets sweaty. Polyester feels more like cotton but can be woven tighter, dries faster and sports higher “denier” — finer threads and more per inch.
A little-known secret in the UPF wars is that unrated fabrics also deliver strong UV blocking capability, but since they haven’t been proved by tests, these can’t use a UPF rating.
How We Tested
Our test process was simpler than that of ASTM International. However, over time, our tests have shown a strong correlation between the UPF rating and UV light penetration. We used a UV light source and measured the unprotected UV light before each test. Then, we spread the fabric over the light source using a frame for consistent distance from the light. Our measuring device is a General UV513AB UVAB light meter. We calculated UV light blockage with this formula:
1 - [UV light transmitted through the fabric ÷ Total UV light] = UV blockage. Note: UV light was measured in nanometers.
ExOfficio JavaTech Polo
UPF Rating: 15
% UV Blocked: 94
S Café technology weaves processed coffee grounds into the fibers to increase moisture and odor control. Nope, no coffee smell, and no cooking smells after a toasty afternoon of charcoal grilling. Its UPF offers a great blend of sun blockage and maximum breathability for comfort. Fast-drying and with a breezy form fit.
Material: 53% cotton, 47% recycled poly
Colors Available: Hydrant, Black, Yam, Cobalt, Dusty Olive
Sizes Available: S - XXL