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Can You Microwave Glass? (Is It Safe?)

Can You Microwave Glass? (Is It Safe?)

Microwaves have been a common household item since the early 1980s, and for good reason. They quickly heat food, warm water, and can defrost frozen items.

However, there are still many questions people have over their usage despite how common these appliances are. One of those many questions is: “can you microwave glass?”

In short, glass can be microwaved and is one of the safer options for microwaves. However, if you plan on using a glass dish in the microwave, you must check to make sure it is “microwave-safe,” which will be inscribed on the bottom of the glass container.

Keep reading to learn more details about what happens to glassware in the microwave and some safety tips to keep in mind.

What Happens When You Microwave Glass?

Microwaves work by heating water molecules in food and vibrating them, which cooks the food. When you microwave glass, it only heats up after an extended time since the formation of glass molecules is similar to water due to its polarity.

In short, food will heat up quicker than glass. Unless you stick a glass cup in the microwave by itself for a long time, it won’t do much other than slowly heat the dish itself.

What Happens When You Microwave Glass

Cold Glass

Cold glass will break in a microwave due to the sudden shift in temperature. Moving rapidly from a low to high temperature will make the molecules in the glass shift, causing it to break.

You can avoid this by only using room-temperature glassware and waiting for the cold dish to warm up before microwaving.

Glass can break in the microwave multiple ways, but each way is due to a different reason. It’s essential to know the warning signs of potentially broken glass.

Cold Glass

Glass With Bubbles Inside

Due to manufacturing errors, there may occasionally be tiny air bubbles trapped in the glass. These will usually be at the top or the bottom of the glass container and will either be in a cluster or a single large bubble.

When you see bubbles in your glass, you don’t need to throw it away. You can still use it instead for non-heating purposes, such as in the fridge.

Frozen Glass

This form of glass is cold and has excess water all over it to keep the heat. Like cold glassware, they have an even higher tendency to shatter when put into immediate heat after being frozen.

For this reason, you should completely thaw all forms of frozen glassware before microwaving them, just to be on the safe side.

Non-Microwave-Safe Glass

While it’s safe to microwave most types of glass, you’ll want to check the bottom of all glassware to see if there is a microwave-safe emblem.

Some dishes will not have this symbol, which is a warning that the container has different properties than typical glass. If there is no warning, use the water test to check.

How to Test if Glass Is Microwavable

Occasionally, there will be times when there is no “Microwave-Safe” icon on the bottom of your glassware.

If this is the case, follow these steps to find out:

  1. Take the unsure dish with another glassware dish and put them into the microwave.
  2. Fill the glassware dish with about a cup of water. Do not put any water in the unsure dish.
  3. Turn the microwave up to its highest setting, then put the timer on for one minute.
  4. Wait until the minute is up before moving to feel the dish in question. Be careful during this step, so you don’t burn yourself.

If the dish in question is warm, and the glassware with the water is hot, it’s non-microwavable.

If the dish is cold, but the glass of water is hot, then it’s microwaveable.

Extra Tips for Microwaving Glassware

Since microwaving has special rules, here are some dos and don’ts to keep in mind when you heat something in a glass dish.

Frozen Glass

Don’t Use Aluminum Foil or Styrofoam With Glass

You should always avoid using aluminum foil in the microwave, so the same applies to using it with glass. Since foil will catch fire in the microwave, this fire could cause the glass to melt if it gets hot enough.

It could cause excess smoking and melt the entire inside of the microwave.

Styrofoam should never go in the microwave because it catches on fire like aluminum foil. With styrofoam, however, it melts while it burns.

This means that the heat is sticky and will attach to the glass. With the two burning, shattering, and mixing, they could cause serious injury to anyone who would touch it.

Along with this, the smoke and smell have dangerous qualities as well.

Get a New Microwave if It Breaks

Recent microwaves have special programming so they don’t reach temperatures that cause glass to melt or break. However, if they become broken or damaged, it could cause problems.

If you feel like your microwave isn’t working correctly, make sure to change it out with a new model to keep yourself safe.

Stir the Food Throughout Cooking

While you’re cooking and using a glass container or any container in the microwave, make sure to stir the food throughout cooking it. This will ensure that the food’s heat distributes evenly over the container’s bottom.

A general rule is to stir food halfway through all microwaved time.

Related Questions

Here are some quick answers to other questions people ask about microwaving glass.

Can you microwave glass?

Yes, you can microwave glassware as long as it has a microwave-safe icon on the bottom and is not cool. However, these dishes can shatter when placed in the microwave if they get knocked over or become too hot.

Glass With Bubbles Inside

How can I test unmarked glass for the microwave?

To test if your dish can be microwaved, put it into the microwave dry with another microwave-safe glass container filled with a cup of water. Microwave both for one minute.

If both dishes are warm, you shouldn’t microwave the unmarked dish.

However, if one is cold while the other is hot, you can microwave the mystery glass.

What types of glass will break in the microwave?

The situations that cause a glass to break come in different aspects of the dish’s shape. If the glassware has bubbles, is frozen, or is non-microwave safe, it will break or shatter when used in the machine.

What happens when you microwave glass?

When you use a microwave, the water molecules in the food vibrate to heat up. Since glass is very different from food products and other materials, its molecules will not vibrate and make it hot.

It will only get hot from the food it’s holding.

Therefore, when you microwave glass, nothing happens unless it’s not a designated microwave-safe dish.

What do I do if my glassware shatters in the microwave?

If you’re ever in a situation where glass breaks in the microwave, wait until the food and glass are cool before cleaning up. Ensure that the spinning disk at the bottom of the microwave isn’t damaged while cleaning up.

Throw away both the food and the glass, and check for any sharp pieces laying around before using the microwave again.


Be sure to check for the microwave-safe icon on the bottom of your dish before using it in the microwave. Glass won’t typically break in the microwave unless there is a problem with it, such as bubbles, being too cold, or being a non-microwave-safe dish.

If you are ever unsure of if a glass is safe in the microwave or not, you can always check with the method above.