Sunglasses: You Are Paying for Hinges, Not Lenses

UV400 appears on nearly every pair of sunglasses sold in North America, from four dollars to four hundred. It is close to meaningless as a purchase signal.

Where the money actually goes

Acetate frames are cut from sheet cellulose and finished over many stages of tumbling and polishing; injection-moulded frames are shot into a mould in seconds. Acetate holds an optician’s heat adjustment, takes a repair and does not go brittle with age. Moulded plastic does all three badly, which is why Ray-Ban and Persol still cut acetate at this price.

The hinge is the failure point

A hinge is opened and closed several times a day for years, which makes it the most worked part of a pair of glasses and the first to go.

There are two kinds. A metal barrel hinge is riveted or heat-sunk into the frame and turns on a pin through interlocking knuckles; it can be tightened, and an optician can replace it. A plastic pin hinge is moulded into the arm — when it snaps, and it snaps at the thinnest point, the frame is finished. Barrel hinges are standard on acetate frames and largely absent from the cheapest moulded ones, which is most of what separates their lifespans.

What to check before you buy

Three things, in order: whether the frame is acetate or injection-moulded, whether the hinge is a metal barrel or a plastic pin, and whether the arms can be heat-adjusted by an optician. Everything else is styling.

If you are buying accessories to keep rather than replace, the same construction-first logic applies to bags and boots.