Lens picker · CR-39
CR-39 or polycarbonate?
Two materials, sold at almost the same price, that win on opposite things. CR-39 is the clearest common lens material and the heaviest. Polycarbonate is impact-rated and thinner, and shows more colour fringing than anything else on the shelf.
Abbe 58 against Abbe 30
The Abbe number measures how much a material splits white light into its colours. CR-39 sits at 58, the highest of the common plastics. Polycarbonate sits at 30, the lowest. The difference shows as a coloured edge on high-contrast lines — a black window frame against a bright sky, headlights on a wet road — seen through the outer parts of the lens rather than through the middle.
It is a property of the material and no coating changes it. A lens is either made of a material that splits light a lot or one that splits it a little.
Weight
Polycarbonate is the lighter material per unit of volume and is also thinner for the same power, so a finished polycarbonate lens is noticeably lighter on the nose than the CR-39 equivalent. At low powers in a small frame the difference is a few grams and nobody notices. In a large frame at a strong number it is the difference people mean when they say a pair feels heavy.
Trivex is lighter than either and sits between them at Abbe 43, which is why it exists.
Impact
Polycarbonate was developed for safety glazing and does not shatter; it is what safety standards for sports and occupational eyewear are written around. CR-39 chips and can crack, which is why shops decline to cut it for rimless mounts, where screws pass through the lens itself, and for children's sports frames.
For an ordinary full-rim pair worn at a desk, impact resistance is a specification neither of you will ever test.
When each one wins
CR-39 wins for an everyday adult pair below about 3.00 D in a full-rim frame, where its clarity is the thing you actually experience and its weight is a few grams. It also wins for anyone who drives at night and notices fringing around lights.
Polycarbonate wins where the lens has to survive something: children's glasses, sports frames, rimless and semi-rimless mounts, and safety eyewear. It also wins where the frame is large and the number is moderate, because the thickness difference stops being theoretical.
The "plastic" naming confusion
Order forms call CR-39 "plastic", "standard plastic" or "1.50", and call polycarbonate "poly" or sometimes also "plastic", because both are plastics and neither is glass. CR-39 itself is a trade designation for a thermoset resin — Columbia Resin number 39 — that has been the default lens material since the 1940s.
If a form offers "plastic" against "polycarbonate", plastic means CR-39. If it offers an index number instead, 1.50 means CR-39 and 1.59 means polycarbonate.
Common questions
Is CR-39 better than polycarbonate?
For clarity, yes: Abbe 58 against 30, which is the largest optical difference between two materials on the same order form. For impact resistance and weight, polycarbonate. Neither is better overall, and the frame and the power decide which difference you will actually notice.
Are CR-39 lenses the same as plastic lenses?
On most order forms, yes. "Plastic", "standard plastic" and "1.50" all mean CR-39, a thermoset resin that has been the default lens material since the 1940s. Polycarbonate is also a plastic, which is where the naming confusion comes from.
Is polycarbonate bad for night driving?
It shows more colour fringing around point light sources than any other common material, because of its Abbe number of 30, and that is what people report at night. Whether it bothers you depends on how far off the lens centre your gaze travels.
What is Trivex, and is it better than both?
Trivex is impact-rated like polycarbonate, lighter than either, and sits at Abbe 43 between them. Its thickness is close to CR-39 rather than polycarbonate, and shops charge more for it. It is the compromise order rather than a material that wins outright.
Run it on your own numbers
Set what the glasses are mostly for below, put your own numbers in, and the picker marks which material row your combination lands on.
Prescription
Copy the numbers exactly as printed. Blank boxes are fine.
| SPH | CYL | AXIS | ADD | |
|---|---|---|---|---|
| OD | ||||
| OS |
Mostly for
Frame
Age band
The "mostly for" tap is where this page starts: it decides which way the clarity-against-thinness trade falls.
Nothing leaves your phone. The paper is only used on this page.
The rest of the picker
EndMyopia treats myopia as a refractive state, not a medical condition. This is a free educational tool — not medical advice, diagnosis, or a substitute for a licensed optometrist. Your optician sets your correction and the shop grinds the lenses.
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