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3. Do You Want Polycarbonate Lenses?
Plastic lenses for sunglasses come in several flavors, including polycarbonate (PC), CR-39, and some proprietary materials. Polycarbonate is the best choice for action sports. Sunglasses made for the military (e.g., those from Wiley X, Smith, and Oakley) are invariably made with polycarbonate (PC) lenses. In fact, any premium sunglasses made to withstand occupational hazards are made with polycarbonate. If there’s a chance of a pebble flying into your eyes, of your taking an endo, or (heaven forbid) a chance of fragments from bullet fire hitting your eyes, you want PC lenses. For mountain biking, river rafting, rock climbing, volleyball, baseball, even golf, you want polycarbonate lenses.
Only polycarbonate lenses stand a chance of passing both ANSI Z-87.1 tests for impact resistance. In one test, a 25mm steel ball gets fired at a lens mounted on a face form. In the other, a pointed, 1.1-pound weight is dropped on a lens, also mounted on a face form. To pass, the lenses cannot shatter AND cannot make contact with the face form. The frame has to hold the lens in place, which means that the sunglasses must be very carefully designed and constructed. Cheap shades made from PC lenses are very unlikely to pass that latter test.
As for acuity, polycarbonate can approach the optical clarity of glass, but only when in the hands of a manufacturer with outstanding quality control. Oakley and Wiley X make great shades using PC exclusively. But cheap polycarbonate sunglasses can be dreadfully, eye-strainingly bad.
The downside of PC? Mainly its susceptibility to scratching. The best lenses receive a scratch-resistant coating that works well, but it can’t turn plastic into glass. Lousy PC lenses will scratch like crazy.
