Before lightweight plastics took over the eyewear industry, glass was the standard lens material — and it hasn’t disappeared entirely. Both glass and plastic lenses are still around today, each with real trade-offs worth understanding before assuming one is simply the “old” option and the other the modern default.
Glass lenses
Glass offers exceptional optical clarity and is highly scratch-resistant compared to most plastics, which is part of why some people who wore glass lenses decades ago still remember them as sharper than anything since. The real drawbacks are weight and fragility — glass lenses are noticeably heavier than plastic, less comfortable over a full day of wear, and shatter rather than crack under serious impact, which is a genuine safety concern that led most of the industry to move away from them.
CR-39 plastic lenses
CR-39, the standard plastic used since the 1940s, is roughly half the weight of glass, more impact-resistant, and easier to tint or coat. It doesn’t naturally match glass’s raw scratch resistance, which is why most plastic lenses today come with a scratch-resistant coating applied during manufacturing rather than relying on the base material alone. For most people, the combination of lighter weight and genuinely improved safety makes plastic the more practical everyday choice.
Which one actually makes sense today
Modern high-index plastics have closed much of the optical quality gap that once favoured glass, while remaining lighter and safer. Glass still has a small niche — some people with very specific optical needs, or a preference for its particular clarity, still choose it — but for the overwhelming majority of everyday prescriptions, plastic (in one of its many modern forms) offers the better balance of comfort, safety, and performance, which is exactly why it became the default in the first place.