Glasses frames are the structure that holds your lenses in place and keeps them positioned correctly in front of your eyes. They’re made up of several interconnected parts, built from a range of materials, and come in different construction styles that affect everything from comfort to which prescriptions they can support. Understanding how frames work helps you pick a pair that fits well, lasts, and suits your needs.
Parts of a Glasses Frame
Every frame has the same core anatomy, whether it costs $30 or $500. The frame front is the main piece that holds both lenses. It includes the bridge, the arched section connecting the two lens openings that sits across your nose. The bridge is the primary contact point between your face and your glasses. It distributes weight, keeps everything level, and largely determines whether your glasses stay put or slide down throughout the day.
The temples are the long arms that extend from the frame front and hook behind your ears. They’re what most people call the “arms.” At the outer edges of the frame front, end pieces connect to the temples through a hinge mechanism, allowing the arms to fold flat when you store your glasses.
Nose pads are the small cushioned pieces that rest on either side of your nose. On plastic frames, they’re usually molded directly into the bridge as a single smooth surface. On metal frames, they’re separate components attached by small adjustable arms, which lets an optician fine-tune the fit.
How Bridge Design Affects Fit
Not all bridges are shaped the same way, and the design you choose matters more than most people realize.
A saddle bridge is the most common type on plastic and acetate frames. It’s a smooth, curved piece that follows the natural shape of your nose, spreading weight across a larger area. This tends to feel comfortable and gives frames a clean look without visible pads.
A keyhole bridge looks like an old-fashioned keyhole: wider at the top, narrower at the bottom. Instead of resting on top of your nose, it distributes weight onto the sides. That makes it a better option if you have a wider or flatter nose bridge, since it doesn’t press down from above.
A double bridge adds a second bar running across the top of the frame above the main bridge. That extra bar provides structural support, making heavier frames feel more stable and distributing weight more evenly.
Bridge width (the gap between the two lenses) typically ranges from about 14mm to 22mm. If your nose is narrower or your eyes sit closer together, you’ll generally need a smaller bridge width in the 14mm to 18mm range. Wider noses or wider-set eyes call for 18mm and above.
Frame Materials
The material your frames are made from determines their weight, durability, flexibility, and price. Most frames fall into two broad categories: metal and plastic.
Metal Frames
Titanium is the premium option. It’s very strong, lightweight, and corrosion-resistant. It’s also hypoallergenic, which matters if you’re allergic to nickel or other metals. Titanium frames hold up well under rough use, making them a solid choice for active people or older kids who are hard on their glasses.
Stainless steel is lightweight and strong, though not quite as light as titanium. It resists corrosion and tends to cost less than other metal options. If you’re avoiding nickel, look for frames specifically labeled “nickel-free,” since not all stainless steel is nickel-free by default.
Plastic Frames
Acetate (sometimes called zyl or zylonite) is the most popular plastic frame material. It’s inexpensive, lightweight, and available in a huge range of colors and patterns. Opticians can adjust acetate frames easily by heating and reshaping them. The tradeoff is that plastic frames break more easily than metal ones, and over time the color can fade slightly and the material may lose some strength.
TR-90 is a thermoplastic that’s extremely flexible and lightweight. It bends under pressure and springs back, making it popular for sport frames and everyday wear. It has a slightly rubberized feel that grips well during movement, and it’s hypoallergenic. TR-90 handles temperatures up to around 110°C before deforming.
Ultem (a polyetherimide plastic) is stiffer and stronger than TR-90, which lets manufacturers mold it into very thin, wire-like designs that still hold their shape. It resists chemicals, sweat, and corrosion exceptionally well, and can withstand temperatures up to 170°C. You’ll often see it in minimalist sport and lifestyle frames.
Full-Rim, Semi-Rimless, and Rimless
Frames come in three basic construction types, and each one handles prescriptions differently.
Full-rim frames enclose the entire lens within the frame structure. They’re the sturdiest option and the best choice for strong prescriptions, since the surrounding rim hides thicker lens edges and provides extra support. If you have thick lenses, full-rim frames are almost always the recommendation.
Semi-rimless frames (also called half-rim) have a frame along the top of the lens, while the bottom edge is held by a thin nylon wire. They look lighter and more open than full-rim styles, but they expose the lower edge of the lens. For thicker prescriptions, that exposed edge can be noticeable and slightly less durable.
Rimless frames remove the surrounding structure entirely. The bridge and temple arms attach directly to the lenses through small drilled holes or mounting points. They’re the lightest and most minimal-looking option, but opticians generally recommend them for lighter prescriptions. Thick lenses in rimless frames look bulky and are more vulnerable to chipping at the mounting points.
Hinges and How They Work
The hinges connecting the temples to the frame front take more abuse than any other part of your glasses. Standard barrel hinges use a simple interlocking mechanism with a small screw. They’re reliable but rigid: the temples open to roughly 90 degrees and stop.
Spring hinges allow the temples to flex outward past 90 degrees. They create softer, consistent pressure on the sides of your head that self-adjusts based on your head width. This makes them more comfortable for people who put their glasses on and take them off frequently, since the outward flex reduces stress on the hinge each time. Spring hinges also tend to have better long-term durability because that flexibility absorbs force that would otherwise loosen a standard hinge over time.
Frame Sizing
Glasses frames are measured in millimeters, and three numbers define the size. The first is lens width, which is the horizontal measurement of each lens opening. The second is bridge width, the distance between the two lenses. The third is temple length, measured from the hinge screw to the tip of the arm. A frame marked 52-18-140 has 52mm lenses, an 18mm bridge, and 140mm temples.
These numbers are usually printed on the inside of one temple arm. Knowing your measurements makes online shopping far more reliable, since you can compare new frames against a pair that already fits you well.
Skin Sensitivity and Frame Choice
If your skin reacts to certain metals, nickel is the most likely culprit. Frames labeled “100% titanium” or “beta titanium” are common choices for people avoiding nickel. Some stainless steel frames are marketed as nickel-free or hypoallergenic, but you’ll want to check the product description for that specific language rather than assuming.
Non-metal frames like acetate, TR-90, and nylon blends sidestep the issue entirely, since there’s no metal touching your skin (aside from the hinge hardware). Some brands advertise “hypoallergenic acetate” or “BPA-free” materials, though it’s worth knowing that “hypoallergenic” is a marketing term rather than a regulated medical designation.
3D-Printed and Custom Frames
A growing number of brands now use 3D printing to build frames tailored to individual faces. The process typically starts with a 3D scan of your head, and some companies use AI-driven design to create frames adjusted to your facial geometry with millimeter precision. The result is extreme lightness, flexibility, and a fit that’s difficult to achieve with mass-produced frames. Because frames are built to order, the process also reduces overstock and manufacturing waste compared to traditional production.