Which lens material is the heaviest?

The heaviest lens material among the given options is high index glass. High index glass is designed to have a higher refractive index compared to standard materials like plastic and CR-39. This higher refractive index allows lenses to be thinner while maintaining the same optical power, which is beneficial for individuals with strong prescriptions. However, this design feature comes at the cost of increased weight, as glass is inherently denser than its plastic counterparts.

In contrast, plastic and CR-39 lenses, which are lighter and more impact-resistant than glass, are commonly used for their comfort and ease of handling. Polycarbonate lenses, while also lightweight and providing good shatter resistance, are still not as heavy as high index glass. Therefore, high index glass is recognized as the heaviest option due to its density and material properties.