The result is a material that is not only waterproof but is able to block out UV radiation from the sun to such an extent that it would rate a Ultraviolet Protection Factor (UPF) of 101.15 if the chart went that high.
Some Class 2 lenses beat the standard: Avaira, for example, block at least 75% of UV-A radiation and 99% of UV-B radiation, according to the package insert.