CR39 is the abbreviated name of the lens material. CR39 is a plastic optical lens material with a refractive index of 1.498 (usually rounded to 1.5). It is the most commonly used plastic lens material. CR39 has replaced glass lenses as it is much lighter in weight and is safer than glass as it won't shatter or smash if dropped. Like all plastic lenses, CR39 is softer than glass and will scratch easier but it is difficult to smash.

CR39 stands for Columbia Resin 39, which is a lightweight, impact-resistant plastic material commonly used in the production of eyeglass lenses.