As the days get longer and the sun gets stronger we’ve been getting a lot more folks in looking for UPF clothing. Many companies producing sun-specific products will attach a number to the garment that gives you an idea of the protection factor but this is really only a small piece of the story. To understand where the UPF ratings come from you must look at the piece from design to manufacturing to end use.
A common misconception is that UPF is a textile additive that can be applied to a garment much like a sunscreen or DWR. In fact UPF, or Ultraviolet Protection Factor, is a number calculated based on four main points:
Construction: A short sleeve t-shirt will naturally have a lower UPF rating as compared to a long sleeve shirt. Comparing apples to apples the long sleeve will allow less UV light to reach the skin.
Color: A darker color will absorb more UV light than a lighter shade. Even variations within the same color will perform differently.
Treatments: In certain cases a company will opt to treat a garment with a chemical additive that helps reflect the sun’s rays. While UPF can be based on an additive treatment, not all UPF clothing is treated.
Material: Certain fibers outperform others. A nylon or polyester textile will block more UV light than a cotton textile. The density of the weave also plays a large part in the calculation. The closer together the fibers, the less light can penetrate.
All clothing has a UPF. A basic cotton tee, for example, will come in somewhere around 5 UPF providing the wearer almost no protection. Clothing with 15-20 UPF will provide a moderate amount of protection, 25-35 is considered “very good”, while a UPF of 40 – 50+ will be the highest level possible with less than 2.5 % UV transmission.
The proper UPF can make a big difference in your outdoor pursuits but don’t get lured into a false sense of security. Keep up with the sun screen, don’t forget the hat, and drink up!