Glass wasn't strong enough. Polycarbonate wasn't clear enough. Neither material allowed for adequate customization of tints and Light Transmission Levels. So Kaenon set out to develop their own, completely new polarized lens material. Kaenon's proprietary SR-91 is the only polarized lens that combines the superior optical quality of the finest glass and the lightest weight, strength and impact resistance of polycarbonate. Only the best properties. No compromises. No short-cuts.