What is a characteristic of CR-39 lens material?

CR-39 lens material is known for being a type of plastic that is generally more affordable and can be thicker and heavier compared to other lens materials, particularly high-index plastics or polycarbonate lenses. This characteristic often leads to it being considered a budget-friendly option, making it popular for standard prescriptions but not the best choice for those requiring thinner, lighter lenses especially at higher prescriptions.

While it does have some benefits, such as good optical quality and UV protection, it is less scratch resistant compared to other materials like polycarbonate or high-index lenses, which are designed to be more durable. Thus, the description of CR-39 as cheaper, thicker, heavier, and less scratch resistant encapsulates the essence of what this lens material is known for.