7 Ways to Tell if Your Glasses Lenses are Made of Plastic or Glass

When you get a new pair of glasses, more often than not the last thing on your mind is the material of your lenses. You think about your optometrist appointment, then holding onto your prescription, then choosing your new frames and all the perks like anti-reflective or anti-fog coating, then you’re wearing them and that’s that. However, what the lenses are made of matters a surprising amount in how you treat them, the products you can use on them, and how they can be repaired in the event of scratches or frame damage. Do you know what the default is for your personal lens crafter? Are you wearing plastic or glass lenses?

Whether you’re investigating your current pair of glasses or an ancient pair you found in your attic, finding out if the lenses are plastic or glass doesn’t take a science degree, just a few investigative techniques. Here are seven quick ways to test your lens material.

1) Tap it With a Small Metal Object

One of the most easily noted differences between plastic and glass is how the material transmits sound on light, sharp impact. Plastic is softer and doesn’t resonate the same way glass does when struck. Glass is known for that distinct ringing sound or a soft *tink* at the very least while plastic will almost always render a soft *thud* even for gentle taps. To perform this test, take a small rounded metal object like a penny or wedding ring. Hold the glasses by two fingers on one earpiece so as not to interfere with resonance and gently tap one of the lenses. If the sound is clear and high-pitched, the lenses are most likely glass, but could possibly be very hard plastic.

2) Check the Temperature

Glass and plastic serve many of the same functions but with some very distinct differences. Not only are they noticeably dissimilar in the way they transfer sound, they also handle temperature in drastically different ways. Glass is a lot more like thin, smooth rock, holding heat and cold much more efficiently than plastic which tends to resist any significant temperature change. If you live in a cooler climate, glass lenses will be noticeably cold to the touch while plastic will seem like a neutral temperature. If you live somewhere warmer, put the glasses in the fridge for about five minutes. If the lenses are cold when you take them out, they are probably made of glass.

3) Count the Scratches

One of the major differences between plastic and glass is surface hardness. What makes plastic more popular, it’s resistance to shattering due to an inherent softness, also makes them much more likely to scratch, which is why plastic lenses usually come with some kind of anti-scratch coating. If you’re dealing with very old lenses, they may not have this coating and a large number of scratches indicates that they are much more likely to be an old model of plastic lenses.

4) Tap Your Tooth

Sometimes a method is popular because it is easy and always readily available. The question of “Are my lenses glass or plastic?” has existed since plastic lenses were first invented and there is one test method that has been passed down through the generations that has reasonably reliable results. All you need to do is tap a lens against your teeth, a tool that’s always available. If the lenses make a soft ringing sound, they are more likely to be glass. If they make a soft *thunk*, then they are definitely plastic.

5) Check the Weight

Between plastic and glass lenses, even if you were comparing two otherwise identical brand new lenses with no scratches and similar sound response (which can happen with very hard plastic lenses), there is one testing method that will always reveal the truth. Glass is inherently heavier than plastic which is one of the reasons it can reach higher indexes. The heavier the lenses are, the more likely that they are glass as opposed to plastic, especially if they weigh significantly more than the frames.

6) Ask an Optician

If you really can’t figure it out or want to be absolutely sure before using a product that’s rated for only glass or only plastic, you can always ask someone whose job it is to know lenses inside and out. This professional is your optician. What’s an optician? They’re not the person that tests your eyes. Rather, an optician is the nice person in the glasses shop who helps you pick a pair of frames, marks where the center of focus is on each eye, and helps you fit the glasses to your face when they finally come in. These opticians are also used to talking to people about choosing high index lens types, specific lens materials, and choosing the right combination of coatings for each person’s vision needs. With all this expertise combined, they should be able to tell you if the mystery lenses are plastic or glass at the very least.

7) Try to Scratch Them

The final method, which you may not want to try but might be fun if you’re working with an old pair you don’t plan to wear is to literally test the scratch resistance. Rather than simply counting the scratches and guessing, take a small sharp knife and try to mark the edge of one of the lenses. If you can easily create a scratch, then it’s definitely plastic. If not, then they are most likely glass or, once again, hard plastic.

In order to treat your glasses properly and know what to do if they get damaged, it’s important to know exactly what they’re made of. Just like you wouldn’t want to leave plastic frames in the car, lest they soften and get misshapen, you don’t want to use the wrong scratch repair on your glass lenses. For more helpful glasses tips and tricks, contact us today!