Orma® is Essilor's version of CR39 which was for many years, the world's most popular lens material. Orma® is a lightweight, tough plastic lens that is much safer than glass.It weighs far less than the equivalent glass lens and it very easy to tint. Hard coatings are recommended to increase scratch resistance and anti-reflection coatings can be applied.
For ophthalmic optics, CR39 features a number of properties which account for its success : a refractive index of 1.5 (close to that of standard glass), a density of 1.32 (almost half that of glass) and a constringence of 58-59 (thus a very low chromatism), high impact resistance, excellent transparency, and multiple tinting and coating possibilites. Its major drawback is its limited resistance to abrasion relative to glass.
Refraction Index: 1.50
Protection: 93% UVA-UVB 100%
Filtration of UV: 355 nm