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What Is CR-39 Lens Material?

CR-39, which stands for Columbia Resin #39, is the most common material used for prescription eyeglass lenses. Developed by the Columbia Resin company in 1940, it was the 39th formula in a series of thermosetting resins. Originally intended for fuel tanks in military aircraft, its optical properties were found to be so superior that it revolutionized the eyewear industry by the late 1940s. It remains the standard "plastic" lens against which all other lens materials are measured.

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What Is CR-39 Lens Material?

CR-39, which stands for Columbia Resin #39, is the most common material used for prescription eyeglass lenses. Developed by the Columbia Resin company in 1940, it was the 39th formula in a series of thermosetting resins. Originally intended for fuel tanks in military aircraft, its optical properties were found to be so superior that it revolutionized the eyewear industry by the late 1940s. It remains the standard "plastic" lens against which all other lens materials are measured.

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Optical Clarity and the Abbe Value

The primary reason CR-39 is still used today is its exceptional optical quality. In the world of optics, clarity is measured by the Abbe value. CR-39 has an Abbe value of 58, which is nearly as high as crown glass. This high value means the material has very low chromatic aberration, the phenomenon where light disperses and creates color fringes around objects. For the wearer, this translates to crisp, clear vision without the "rainbow" effects or peripheral distortion often found in higher-index materials like polycarbonate or high-index plastics.

Material Properties: Thermoset vs. Thermoplastic

CR-39 is a thermosetting plastic, which means it is cured by heat in a chemical reaction that permanently changes its molecular structure. Once the lens is cast, it cannot be melted or reshaped. This provides excellent dimensional stability; the lenses will not warp or distort when exposed to heat. This is a significant advantage over "thermoplastic" materials like polycarbonate, which can be more prone to internal stress and optical inconsistencies during the manufacturing process.

Weight and Durability Compared to Glass

Before CR-39, most lenses were made of glass. While glass has excellent clarity, it is heavy and dangerous if shattered. CR-39 provided a major breakthrough by being approximately 50% lighter than glass while offering much higher impact resistance. While it is not as impact-resistant as polycarbonate or Trivex, it is significantly safer than glass. Its surface is also naturally more resistant to scratching than most other plastics, although modern CR-39 lenses are almost always treated with an additional hard scratch-resistant coating for longevity.

Prescription Limitations

The main drawback of CR-39 is its refractive index of 1.498. Because this index is relatively low, the material is not "thin." For individuals with high prescriptions, CR-39 lenses will be significantly thicker and heavier at the edges than high-index alternatives. Consequently, CR-39 is typically recommended for patients with lower prescriptions (between -2.00 and +2.00) or for those who prioritize the highest possible visual clarity over the aesthetics of thin lenses.

FAQs on CR-39 Lenses

Do CR-39 lenses have UV protection?

Inherently, CR-39 only blocks about 80% of UV rays. Therefore, an additional UV-protective coating is usually required to ensure 100% protection from UVA and UVB light.

Can CR-39 be tinted?

Yes. Because of its molecular structure, CR-39 accepts tints very easily and evenly. This makes it a popular choice for custom sunglasses and fashion tints.

Are they good for rimless glasses?

No. CR-39 is relatively brittle. When holes are drilled into it for rimless or semi-rimless frames, the lens is prone to cracking or chipping around the drill sites. Trivex or polycarbonate is preferred for those frame styles.

When to Choose CR-39

If you have a mild prescription and your primary goal is the sharpest vision possible at an affordable price, CR-39 is the ideal choice. It is the best material for budget-conscious buyers who do not want to sacrifice the visual quality that high-end optics provide.

References

https://www.aao.org/eye-health/glasses-contacts/eyeglass-lens-materials-guide
https://pubmed.ncbi.nlm.nih.gov/11064942/
https://www.sciencedirect.com/topics/engineering/columbia-resin