Materials
TR90, polycarbonate or metal: what glasses frames are actually made of
TR90: the one that bends
TR90 is a thermoplastic nylon that flexes under load and springs back, which is why the square 3-packs survive back pockets and toddler grabs. It is also light: a full 3-pack weighs about 3.5 ounces, so a single frame runs close to one ounce. The finish is matte and slightly warm to the touch. Weak point: sustained heat, which is why the care rule about parked cars exists. If glasses in your life get sat on, this is the material.
Polycarbonate: the multipack economist
Polycarbonate frames mold cheaply and precisely, which is what holds a 5-pack of readers under $20. Stiffer than TR90, so a hard bend is a break rather than a flex, but at four spare pairs per order the math forgives. Color options are widest here, which is why the mixed-color packs are polycarbonate country.
Thin metal: the retro featherweight
The round metal rims are the thinnest profile in the catalog and carry adjustable nose pads, the one fit feature plastic frames skip. On the face they disappear; wearers of the original round metal pair cite the weight as the reason it became the daily. Metal takes one careful bend for fit and holds it, but repeated rebending fatigues the rim. Finishes run matte black, gold and tea leopard.
Fit numbers that matter
Most frames here measure 51 to 52 mm across the lens with a 14 to 15 mm bridge and medium sizing overall; the snug-on-wide-faces note in the ratings traces to exactly that. Compare against a pair that already fits: the numbers are printed inside almost every temple arm on glasses you own. TR90 and polycarbonate rest on molded pads, so if your nose prefers adjustable pads, that is the metal shelf.
Material second, job first
The lens decides the shelf: zero-strength for screens (the blue light guide), a diopter for print (the strength guide). Then material by habit: TR90 for rough handling, polycarbonate for spares in every room, metal for the lightest thing on your face. All three carry the same UV400 coating and answer to the same care routine.
