All safety glasses that are certified by OSHA utilize polycarbonate lenses. Polycarbonate offers a number of benefits that are useful in hazardous working environments including UV protection, impact resistance, and scratch resistance. They are also typically thinner, lighter and will not shatter on impact. Polycarbonate is also the preferred choice for high prescription eyewear.
Plastic lenses or CR-39 lenses are used for most prescription eyewear. It is a cost effective, lighter alternative to glass and can be coated to provide scratch resistance, ultra-violet protection and anti-glare qualities. CR-39 lenses can shatter on impact so they generally will not be ANSI Z87.1 certified.