UPF stands for Ultraviolet Protection Factor. The UPF is a rating used to gauge how much UV radiation a piece of fabric allows to reach your skin. Let’s say a hat is made from material with a 30 UPF rating. This means the hat blocks around 97% of the sun’s UV rays.
The Skin Cancer Foundation gives its seal of recommendation to clothing with a UPF rating of at least 30. And for those keeping score, the Titleist Tour Performance hat boasts a 50+ UPF rating, meaning it blocks more than 98% of sun rays.