Two materials dominate modern sunglass lenses: CR39 and polycarbonate. Side by side on a shelf they look identical; in use they behave like different species. One is the optician’s favourite for pure optical clarity, the other is what safety glasses and sports eyewear are cut from because it refuses to shatter. Knowing the difference takes five minutes and makes you a much sharper buyer — whether you are reviving an old favourite for city wear or speccing lenses for hard outdoor use. Here is the comparison in plain words.
CR39: the optical classic
CR39 is a hard thermoset resin that has been the standard plastic lens material in optical shops for decades, and its appeal is simple: light passes through it very cleanly. It renders sharp detail with little colour fringing at the edges of vision, it takes tint evenly and deeply, and its surface is naturally harder than bare polycarbonate, so it resists fine scratching well. It is also far lighter than glass. The trade-off is toughness. CR39 is rigid rather than resilient: a dropped pair meeting a stone step edge-first, or a hard knock inside a rucksack, can chip or crack it instead of flexing. For a lens that lives a gentle life across a café table, that hardly matters. For one that lives on a trail, it does.
Polycarbonate: the impact workhorse
Polycarbonate earned its place in eyewear through safety glasses, sports goggles and children’s lenses, and it holds that place for one reason: it does not shatter. Where CR39 cracks, polycarbonate absorbs the hit and springs back. It is noticeably lighter than CR39 and can be cut thinner for the same strength, which is why wraparound sports lenses are almost always polycarbonate. It has two honest weaknesses. First, its surface is softer, so an untreated polycarbonate lens scratches easily — which is why quality lenses carry a hard coating that closes most of that gap. Second, in its raw state its optics trail CR39 slightly, with a touch more colour fringing at the extreme edges of vision. Precision cutting and modern coatings narrow that difference to the point where, behind a sunglass tint, almost nobody can tell.
Head-to-head: what actually matters
Weight and all-day comfort
Polycarbonate wins. A lighter lens means less pressure on the nose pads and behind the ears — a difference you notice at hour six, not minute one.
Optical clarity
CR39 by a nose, in laboratory terms. In real terms — through a tinted lens cut accurately to your frame’s curve — the difference at the centre of vision is effectively invisible.
Impact resistance
Polycarbonate, by a distance. It is the reason the material exists in eyewear at all. If a lens might ever meet a branch, a ball or the pavement, this category outweighs the rest.
Scratch resistance
Bare against bare, CR39. Hard-coated — which any lens worth buying is — the two run close. Either way, the microfiber cloth in your pocket matters more than the material.
UV protection
A tie, with a caveat. Polycarbonate blocks UV as an inherent property of the material; CR39 needs a UV-absorbing treatment, which good lenses always include. Either material can meet the UV400 standard — what matters is that yours does.
What our compatible lenses are cut from
Every lens in our compatible replacement lens range uses the material that fits its job: our sun lenses are cut from hard-coated polycarbonate, while our clear lens options use CR39 for maximum optical clarity — and the reasons follow straight from the comparison above. A replacement lens goes into a frame that has already lived one life and is about to live another — worn on trails, dropped on pavements, tossed into bags — so impact resistance is not optional. Polycarbonate blocks UV by nature, so full UV400 protection is built into the material rather than painted on, and its low weight keeps a revived pair comfortable all day. The traditional criticisms — softer surface, slightly lesser raw optics — are exactly what the hard coating and precision cutting exist to solve: each lens is machined to the specific curve and caliber of the model it fits, across both our Ray-Ban-compatible and Oakley-compatible ranges.
So which mindset should you pick?
If a lens lives a quiet indoor life — prescription work, reading, screens — CR39’s clarity-first philosophy is why opticians still reach for it. Sunglasses live harder lives, which is why we side with polycarbonate for every pair we help revive. Remember, too, that material is only one of three decisions: tint and polarization matter just as much, and our guide to polarized vs non-polarized replacement lenses settles the second in plain words. Fitting the result yourself takes minutes with our step-by-step guides to replacing Wayfarer lenses and replacing Holbrook lenses. Free worldwide shipping, a 3-year warranty against manufacturing defects and 14-day returns come standard on every order. SunglassRevivers lenses are independently manufactured compatible parts; they are not products of Ray-Ban®, Oakley® or any frame brand, whose names appear here only as compatibility references. Don’t replace them. Revive them.