CR39

The name comes from Columbia Resin #39 — the thirty-ninth formula tested by PPG Industries in the 1940s. The first thirty-eight did not work. Number thirty-nine did. It has been the preferred lens material for serious eyewear ever since, which makes the clinical name feel like a missed opportunity. Something that good deserved better.

What CR39 does is simple to describe and difficult to replicate. It transmits light with almost no distortion. Colours look correct. Edges stay defined. There is virtually no chromatic aberration — the subtle bending of different wavelengths that makes cheaper lenses feel slightly wrong even when you cannot say why. You may have noticed the effect without knowing the term: a faint tension behind the eyes after a full day in sunglasses, a sense that something is working harder than it should. That is often the lens, not your eyes.

The material that dominates mass-produced eyewear is polycarbonate. It is lighter, cheaper, and more impact-resistant, which makes it the right choice for safety glasses, sports eyewear, and children's frames. For everything else, it is a compromise. Polycarbonate has a slight optical softness that becomes invisible only because most people have never compared it to anything better. Wearing CR39 after years of polycarbonate is not dramatic. It is quiet. You just notice, at some point during the day, that your eyes feel like they have been let off a leash.

There is a reason that nearly every independent eyewear brand with a reputation for optical quality chooses CR39. It is not the newest material on the market. It is not the lightest. It is not the cheapest. It is simply the one that gets out of the way and lets you see clearly. A lens should not remind you it is there. CR39 does not.

When sun tinting is applied to CR39, the colour is absorbed into the lens rather than coated onto the surface. This means the tint cannot peel, wear away, or degrade separately from the lens itself. The colour and the lens are one structure. Whether the tint is a solid grey, a brown gradient, or a green — it stays consistent for the life of the lens, because it was never a layer to begin with.

We chose CR39 because we spent time with the alternatives and kept coming back. The optical difference is not something most people will articulate. But it is something they feel — in the comfort of a long afternoon outdoors, in the accuracy of colour on a bright street, in the absence of the small fatigue that accumulates behind lesser glass. The lens should be the least noticeable part of a good pair of sunglasses. That is exactly what CR39 is. Thirty-eight failures and one answer that has held for eighty years.