Columbia Resin #39, or CR39 as it is known as today, is the 39th plastic polymer formulation to come of the Columbia Resins project in 1940. Like Trivex and Polycarbonate materials, CR39 was developed for military use as a way to reinforce fuel tanks and lower the weight of bomber aircraft. Because the plastic was transparent to the visible light spectrum and because it is half the weight of glass, CR39 was adopted as a lens material and eyeglass wearers have relied on CR39 plastic lenses for more the six decades. CR39 has almost single handedly brought about the near extinction of glass as a lens material.
Like most plastics, CR39 is tough and resists scratching, heat and most chemicals. It is the clearest lens material in common use on the Abbe scale at an average value of 58. Comparatively, Trivex is the next clearest to CR39 at 45, and polycarbonate is 32 (highest numbers are better). Most high index plastic blends fall below an Abbe value of 40.
CR39 is a perfectly suitable material for appearance and aesthetics in many low to medium power prescriptions (Rx). For higher power prescriptive corrections CR39 is will yield the thickest edge profile of any commonly used lens material because of its low index value of 1.50. However, for the right Rx, and carefully considered frames, CR39 can be used with few compromises because of its low cost and otherwise noteworthy qualities. CR39 is not usually the best choice for rimless drill-mount eyeglasses. The superior impact resistance of polycarbonate and Trivex materials are preferred over CR39 for children’s glasses and applications where safety is a primary consideration for the eyewear. However, CR39 is highly colorable/tintable and there aren’t many colors that can’t be accomplished for that fashion look using CR39. For shear bang for the buck, CR39 lens material is unbeatable as a lens material. CR39 can be made into almost any Rx too. When everything is considered, including the superior optical qualities of CR39, it would be difficult to find a better overall material for the majority of wearers than CR39. In high power lens prescriptions, CR39 is usually not the best choice to avoid unappealing edge profiles or thick lens centers.
