CR39 is a thermostable polymer, with high resistance to impacts and protection from ultraviolet radiation. It is resistant to most solvents and other chemicals. It allows any type of treatment (anti-reflective, hardened, mirrored), allowing 100% dye absorption. This makes it easier for the lenses to be colored, so the material is often used for the manufacture of sunglasses.
This type of material has a very low density, this makes the lenses very light, 50% lighter than glass.