What is the highest UPF rating?

That depends on the testing method used to determine the UV levels. In the United States, UPF tests adhere to the American standard AATCC 183, using the sun spectrum of Albuquerque, New Mexico, the same as the European Standard. At Sunday Afternoons, we work with an independent, certified testing agency to evaluate our fabrics wet and dry to verify UPF levels. The majority of our products are rated UPF 50+, the highest possible rating from the AATCC, blocking over 98% of UVA and UVB rays.