Polycarbonate lenses are thinner, weigh less, and are more scratch and impact resistant* than plastic lenses with the same prescription. This makes polycarbonate the smart option for children, sports, and safety glasses.
* No lenses are unbreakable or shatterproof.
High-Index materials are denser and can refract, or bend, light to a greater degree than glass or plastic lenses of the same thickness. The same correction can be gained from a less curved and therefore thinner and lighter lens when made of a High-Index material than glass or plastic.