The NRS Kids' HydroSilk Shortsleeve Shirt is an 8-oz nylon/spandex blend providing a UV protection factor of 50, blocking the sun's harmful UV rays. Much easier than having to keep applying sunscreen! Snug-fitting and lightweight, fits easily under other layers in cooler weather, wicking moisture away from the skin. A silky finish inside and out feels great against the skin, making it easy to keep kids in this shirt for a full day's activities. Great for any activity when sun protection is needed. Sun protective clothing is another option for foiling the sun besides sunscreen, a wide-brimmed hat and sunglasses. These fabrics have a tighter weave or knit and are usually darker in color. The rash guard is a fine example, as the shirt gives you an Ultraviolet Protection Factor (UPF) of 50+. This means that the shirt allows less than 1/50th of the sun’s rays to penetrate the fabric. The typical t-shirt has an UPF rating substantially lower than the recommended UPF 15.