Two lenses, same prescription, one costs a few dollars and one costs a few hundred. The difference is not marketing. It is the material, the design, and the coating stack on top.

Material decides four things: how thick the glasses look, how clear the edges stay, whether they survive a drop, and what you pay per pair. A coating can improve a lens. It cannot fix the wrong material underneath.

This guide covers the materials that Chinese lens factories actually ship in volume, the price band each one falls into, and the points where lens choice and frame design have to agree.

Part 1  |  Four numbers that decide everything

Four numbers that decide everything

Refractive index. Light bends when it enters a lens. A material that bends light harder needs less of it to reach the same prescription, so the lens comes out thinner and lighter. That is the only thing a higher index gives you.

Abbe value. White light is actually a mix of colours, and a lens bends each colour slightly differently. That is what produces coloured fringes at the edge of a strong lens. The Abbe value measures how bad this is. Higher is better. The human eye sits around 58.

Density. Two lenses of the same size, one heavier than the other. Trivex is the lightest optical material in common use, at 1.11 g/cm³. Glass is 2.54, which is why nobody ships glass across an ocean if they can avoid it.

Toughness, not hardness. These are two different things and buyers mix them up constantly. A hard material cracks. A tough material bends and springs back. This one property decides whether a rimless drill-mount pair lasts a year or a month.

Part 2  |  What each material is actually for

CR-39 (1.50): the honest baseline

Colour reproduction is close to neutral, every lab can process it, and it is the cheapest optical plastic there is. For low prescriptions where thickness does not matter and the optics are the whole product, it is still the right answer.

It becomes the wrong answer above ±4.00, in a large frame, or anywhere the lens gets drilled. It scratches without a hard coat, and it does not pass the high-velocity impact test for safety eyewear.

1.56: the volume material

This is what most of the Chinese market ships, usually on domestic monomer. About a tenth thinner than CR-39 at the same power, for a small price step. The problem is consistency, not the index itself.

Good 1.56 and cheap 1.56 look identical on a spec sheet and behave very differently after two summers in a car. One yellows, one does not. Ask for the monomer origin in writing, or you are guessing.

1.60 / MR-8: the safe default

Index high enough to make a visible difference, Abbe still 41 so the optics hold up, tough enough for a semi-rimless groove, and it takes a coating stack cleanly. There is no real weakness here. It costs roughly two to three times 1.56.

If a buyer asks what to use and gives you no other information, this is the answer for anything from ±3.00 to ±6.00.

1.67: where high myopia starts to be solvable

Past −5.00 the edge thickness of a 1.56 lens becomes visible to the customer, and that is exactly where 1.67 earns its price. You pay for it in colour fringing (Abbe 31) and in reflections, which is why 1.67 without AR coating is a waste of money.

It is also brittle. Most labs will not put it in a drill mount, and they are right not to.

1.74: the thinnest, not always worth it

This is the thinnest material that ships in volume. It makes sense above −8.00, or on a product where the customer is paying for the look. Between −6.00 and −8.00 it is a judgement call.

Below −6.00 it mostly is not worth it. You take a fraction of a millimetre off the edge, pay several times more, and lose optical quality at the same time.

Polycarbonate: safety first

About ten times the impact resistance of CR-39, which is why it is the default for children, sport, and wrap frames. It also blocks UV as part of its chemistry, so the protection cannot wear off.

The costs are real. Abbe 30 means visible colour fringing at high powers. The surface is soft and scratches fast. And it stress-cracks around drill holes if it touches acetone, solvent cleaners, or a screw that is too tight.

Trivex: the one most brands underuse

Impact close to polycarbonate, Abbe 45, the lowest density of any optical material, and enough tensile strength to hold a drill mount. For rimless, it is the first recommendation and it is not close.

The cost is the real objection. Industry pricing puts Trivex roughly 45–65% above polycarbonate, and in China it often lands higher than that, because few lines run it. It is also slightly thicker than polycarbonate at the same power, and not every lab keeps it in stock. Plan six weeks, not two.

That premium is still easy to justify on a rimless pair. The alternative is a lens that cracks at the drill hole and comes back as a complaint.

Glass: rarely the answer now

Still sold in Japan, parts of Europe, and some occupational channels for scratch resistance and pure optical quality. It is also twice the weight, it shatters, and each lens needs individual impact testing.

Part 3  |  Matching the lens to the prescription

One number almost nobody quotes

Each step up in index removes only about 7–10% of the edge thickness, at the same power and the same frame. That is because thickness follows 1/(n−1), and the steps between standard indexes are small.

Going from 1.56 all the way to 1.74 is a total gain of about a quarter. Going from 1.67 to 1.74 is about 9%. It is a real gain, but it is not the transformation the catalogues imply.

This matters when you price the upgrade. On a −8.00 the 1.74 looks noticeably better on the face, and the upgrade is easy to sell. On a −4.00 nobody will see the difference, and a wearer who is sensitive to colour fringing may think the new pair is worse.

Part 4  |  Which material for which situation

Part 5  |  Where the money actually goes

We are not going to publish dollar prices, and it is worth saying why. A lens quote moves with monomer cost, with the exchange rate, and with your order volume. Any figure we print is wrong within three months, and it would be wrong for your order on day one, because the price depends on your batch size and your coating specification.

What does hold up is the ratio between materials. Set 1.56 single vision with anti-reflective coating at 1, and read everything else as a multiple of it.

Look at the jump from 1.67 to 1.74. It costs roughly four times as much and removes about 9% of the edge thickness. That single line explains most of the confusion in this category: the most expensive step is also the least efficient one.

It is still the right choice above −8.00, where every millimetre shows on the face. Below that, the customer is paying four times more to fix a problem they cannot see.

Which is why the better question is not “which index” but “what is actually driving this quote”.

Five things that move price more than index does

· Monomer origin. Mitsui and PPG cost more than domestic equivalents, and they behave differently after two summers in a car. That is when yellowing shows up, and that is when returns start.

· Coating stack. A proper super-hydrophobic stack adds roughly 30–60% to the blank price. Moving from 1.56 to 1.60 roughly triples it. The coating costs far less, and the customer notices it more.

· Lens design. A freeform progressive costs five to ten times a stock single vision. You are buying surfacing time and a design licence, not plastic.

· Photochromic chemistry. Activation speed, fade speed and how long the dye lasts vary a lot between suppliers, and the price gap is usually smaller than the performance gap.

· Volume and coating batch. Coating is a batch process. Three hundred pairs and three thousand pairs have different unit costs, even on the same material.

Part 6  |  What else goes on the lens

A modern lens is a stack of thin layers, not a single piece of plastic, and the order matters. The hard coat sits against the lens. The anti-reflective layers sit on top of it. The hydrophobic and oleophobic finishes go last, because they are the layers the cloth actually touches.

If the budget covers only one upgrade, buy the AR coating rather than the higher index. A bare 1.67 lens reflects 7–8% of light at each surface. The gain from thinner edges is partly cancelled by reflections sitting on top of them.

Be careful what you print on the box about blue light. The evidence for an eye-health benefit is genuinely mixed, and several markets now ask for substantiation. The claim that holds up is narrower: it reduces short-wavelength transmission, and some wearers find long screen sessions less uncomfortable. Avoid “protects your eyes” unless you can back it up.

Part 7  |  Frame first, or lens first

Most customers choose the frame first. They try on six pairs and buy the one that looks right. That is not a mistake to be corrected — it is how the category works. The lens has to fit the frame.

Two directions exist, and they answer different questions.

Frame first: the default

This covers most orders. The frame is already chosen, so the job is to find a lens that holds up in it. Five things on the frame decide the answer.

Answer those five and the lens is decided. Nothing on the frame has to change.

Lens first: the exceptions

Three situations run the other way. All three are about helping the customer pick a better frame, not about rebuilding one.

· High prescription, roughly above ±6.00: recommend a full rim, a slightly wider rim and a smaller eye size. Same index, visibly thinner result.

· Refitting old lenses into a new frame: the new frame's eye size cannot exceed the old lens, or it will not go in — whatever the material.

· Function first: a drill mount, a sport pair or a progressive sets the requirement before style does.

That is the whole rule. The customer picks the frame. We make sure the lens is worthy of it.

Part 8  |  The spec sheet to send your factory

If you send nothing else, send this list. It is the difference between a first article that passes and three rounds of samples.

· Material named by monomer where it matters — “1.60 MR-8”, not “1.60”.

· Design: single vision, bifocal, or progressive, with corridor length in millimetres.

· Base curve and blank diameter.

· Coating stack in order, each layer with its test standard.

· Photochromic: colour, category, activation and fade time.

· Tint or mirror: light transmission percentage and tolerance.

· Edge treatment: polished or matte, safety bevel, minimum thickness at groove or drill.

· Packaging: lens bag, axis marks, barcode, and how left and right are paired.

· Standards to certify against: ISO 8980, EN 166, ANSI Z87.1, FDA 21 CFR 801.410.

· Volume, delivery window, and who carries breakage in transit.

FAQ  |  Common questions

Is a higher index always better?  

No. It buys thinness and charges you in colour fringing, reflections and price. Below about ±4.00 the thickness difference is invisible on the face.

CR-39 or polycarbonate for a child?  

Polycarbonate, or Trivex if the budget allows. At that age the impact argument outweighs the optical one, and children are the least likely group to notice a lower Abbe value.

Why do 1.67 lenses look more reflective?  

Reflectivity rises with index. CR-39 reflects about 4% per surface, 1.67 reflects 7–8%. Without AR coating you have paid for a thinner lens and covered it in glare.

Can I use 1.74 in a rimless drill mount?  

You can, and we would advise against it. High-index is hard but not tough, and a drill hole is a stress point. Use Trivex, or polycarbonate with a chamfered hole and nylon washers.

Does blue light coating actually help?  

It reduces short-wavelength transmission. Whether that produces a measurable health benefit is still contested. It is a reasonable comfort feature. It is not a medical device and should not be marketed as one.

What is the cheapest lens that still passes impact standards?  

Polycarbonate. It clears the FDA drop-ball requirement comfortably and usually costs only a little more than 1.56 at volume. If safety is the requirement, there is no reason to use anything softer.

What MOQ should I expect?  

Stock single vision starts at a few hundred pairs per power-and-coating combination. Photochromic colour runs usually want 500 or more. Freeform progressive is quoted per pair with no real minimum, but the unit price drops sharply above 1,000.

Do all plastic lenses block UV?  

No. Polycarbonate, Trivex and the MR high-index materials block essentially all UV below 400nm as part of their chemistry. Untreated CR-39 passes a small amount, so it needs a UV treatment — and a coating can wear off while chemistry cannot.