This is a pretty good summary of traditional glasses frame materials, to which I will add the following unconventional materials used in 3D-printed frames, that I have personally tried to wear quite extensively:
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PLA: lightweight, cheap, forgiving, ubiquitous, reasonably solid and durable, VERY easy to form - and deform - under moderate heat. Don’t leave PLA frames on the dash of your car in the summer or you’ll come back to a gooey mess. You can easily chemically-polish PLA smooth with acetone to make PLA frames very comfortable to wear on your skin for extended periods of time. PLA is a bioplastic made from plant material and is biodegradable, so it’s a good choice if you’re environmentally-minded. PLA has very low toxicity and is regarded as food-safe.
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PETG: a variant of PET - think frames made of the same plastic soda bottles are made of. Slightly stronger than PLA and a bit more tolerant of heat, but harder to polish smooth. Like soda bottles, it’s not terribly environmentally friendly, but glasses frames use very little of it. PETG is also very low toxicity.Very comfortable to wear for a long time if you take the time to polish it.
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PVB: visually stunning. Can be polished to a shiny sheen in seconds - and destroyed just as quickly if you overdo it - with IPA. Clear natural PVB can be made almost transparent! Not that great mechanically, so only use it if you never abuse your glasses and you’re after the aesthetics. Quite comfortable.
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Wood-plastic composite: I’ve only tried wood-infused PLA. It’s substantially weaker than straight PLA and it’s not terribly comfortable to wear for more than 12 hours, but it looks stunninly like real wood with a modicum of sanding with 400-grid sandpaper. If you like wooden items, this one is for you.
That’s the reason why I started making my own frames. The whole new frame ⇒ new prescription ⇒ new lenses ⇒ new fitting, and the fact that frames never stay on the market for very long, is very much by design. And I don’t much like feeling swindled.
Athough, in fairness, even if you do find the exact same frames, no frames are exactly alike. So it’s quite possible that your old lenses wouldn’t quite fit - particularly snap-in lenses. So to the eyewear industry’s credit, there is an element of non-interchangeability with certain frame designs. But frames with screw-rims and wire rims are definitely interchangeable, and clearly it’s in nobody’s commercial interest to let you find replacements for those.
But the real clincher for me was this: it takes weeks to get new glasses. When I need new glasses, I need them right now, not in five weeks.
Making your own frames, provided you have the lenses, makes you totally self-reliant. You need them, you make the same day - the same hour even with 3D printing. What’s more, with 3D printing, It’s trivially easy to adjust the frames to the existing lenses: just change a dimension or two, re-print, and hey-presto, 15 minutes later, you can try the lenses for fit again. And once you have the correct dimensions, you can just re-print those over and over as you routinely break the frames - because hey, you don’t really have to be careful anymore 🙂
You do need to invest the time to learn a CAD program to model the frames if you want to reuse your existing lenses. Or you can go with an existing design someone else made and order a set of lenses for those - not cheap, but they’ll be your last pair of lenses until your prescription changes. Then after that, like you said, a good basic printer is very affordable these days and will pay for itself the first time you need to replace your frames.
One thing about that: I don’t know if this is still valid, but back in the late 90’s / early 00’s, I used to order super-cheap, super-solid - and super bland - frames from French distributor Alain Afflelou that were sold only on the French market (so I’d get friends in France fo buy them for me.)
France has (had?) a cap on the amount paid out by social security on frames, and all opticians in France carry (carried?) something locally called “montures secu” - lit. “social security frames” that were, well, let’s not mince words, designed for the poor with price and durability in mind.
Opticians in France try (tried?) really hard to steer their customers away from the “montures secu”, strongly hinting that if you chose them, you’d look like a poor person. But the truth is, those frames were properly solid, super-cheap and they’re still made today and referenced as standard designs in almost all edging machines.
The last Alain Afflelou pairs I bought some 20 years ago were like 15 euros a pop (I bought a whole bunch of them) and they’re properly indestructible. I still use them on occasions, and when I need new lenses for them, I show them to my optician who’s nowhere near France and they have this Alain Afflelou frame model in their database. Amazing!
So if you don’t want to go the 3D-printing route, that’s maybe something worth pursuing. But like I said, I don’t know if the “montures secu” are still a thing in France.