Common materials for eye-glasses include glass, standard CR-39 plastic, and newer plastics, Polycarbonate and Trivex. This diagram shows how the different lens materials perform. The vertical scale shows the percent of transmittance, with the different wavelengths on the horizontal axis. As we saw above, untreated Glass allows just about all the UV-A and some B through. CR-39 Plastic is better, absorbing about half the UV-A. It can be treated to absorb over 90% of the UV. The newer materials, Polycarbonate and Trivex , absorb over 90% of the UV by themselves. So if your glasses are made out of one of these 2 materials you don’t need additional UV coating. If the lenses are made out of glass or CR-39 plastic, you should consider UV coating if you spend a significant amount of time outdoors.