Many people use glass to prepare food in the microwave, but is it safe?

In this article, I’ll explain whether you can microwave glass without fracturing or shattering.

Can you put the glass in the microwave?

Can you put the glass in the microwave? Generally, when reheating and preparing food in the microwave, glass is safe. It is a stable enough material, similar to ceramic, and will not leach into the food as other plastics can.

However, there are several safety measures to take while using glassware in the microwave. Before using it in the microwave, it is critical to understand the type of glass container.

Continue reading to learn more about using Pyrex and other microwave glass types.

How to tell if something is microwave safe

Many bowls and plates are microwave safe, but if you use the wrong dish, you risk destroying the dinnerware and the meal. Microwaves are good equipment, but you should take a few precautions before using them on your dishes.

Before using a microwave, always check to determine if the dish is microwave safe. Some containers have the potential to break, melt, or scald you. In addition, some containers, such as foil-lined containers, might potentially harm your microwave.

Microwave-safe dishes are helpful for both cooking and storing food.

Containers that do not microwave safe can only be used for storage or serving.

​​1. Examine the Dish

Flip the dish over so that the bottom is facing you. Examine the back of the dish. Many plates and containers have either “Microwave Safe” or “Not for Use in Microwaves” written.

The standard microwave-safe symbol/logo/label denoting a microwave-safe glass container is a little representation of a microwave with squiggly lines.

Continue to Step 2 if this is not indicated.

2. Turn Up The Head

Set your microwave to the maximum power level. The process differs depending on the manufacturer of the microwave. For precise directions, refer to the owner’s manual for your microwave. A “Power,” “Power Level,” “Menu,” or “Settings” button is found on the majority of microwaves. Typically, the highest power setting is used as the default.

3. Add Water

1 cup of water in a glass measuring cup or glass bowl Microwave the cup of water and the plate. Place the cup of water on or within the dish for larger plates and containers. Don’t pour the water into the dish at hand.

4. Set the Time

One minute in the microwave with the dish and cup. If the dish or container is warm or hot after heating, it is not microwaved safely. The plate or container is microwave safe if it is cool and the cup of water is hot. Please remember that if you placed the cup of water on or on the dish, the area around the cup might have become warm. If the dish is microwave safe, the rest of it should be cool.

How microwave ovens work

A vacuum tube known as a magnetron is located inside the microwave oven. The magnetron generates waves reflected within the microwave oven’s metal interior. These waves may flow through many materials such as paper, plastic, and glass, but they are absorbed by food.

These microwaves are electromagnetic radiation. They make the liquid molecules in the food vibrate, generating heat that cooks the food. However, these waves are non-ionizing radiation. In other words, unlike ionizing radiation such as X-rays, they cannot create alterations in human cells.

Microwave ovens cook food thoroughly by activating radiation waves. Before heating the solid portions, these radiation waves act on any liquid. Remember this crucial information the next time you want to pop a container directly from the freezer.

Some concerns with glass

  • The glass that is not microwave safe may have microscopic air bubbles that expand when heated. If the bubbles expand sufficiently, the glass will break.
  • Metal-trimmed glass is not microwave safe. The metal could spark, shattering the glass.
  • Before using colored glass in the microwave, seek a “microwave-safe” label. The dyes used to paint the glass could harm one’s health.

What types of glass can you microwave?

Here’s a brief rundown of which glass varieties you should and should not microwave.

Microwave-Safe Not microwave safe, if not labeled
Pyrex glasswareGlass-ceramics 
Glassware with labels for microwave-safeColored glassware
Glassware that passes the microwave test (test steps listed below)Glassware with metallic or foil trims
Glassware that doesn’t pass the microwave test

To determine if the glass is safe to use in the microwave, it is helpful to understand the various glass varieties.

The glass used for cooking must be both sturdy and safe. Fortunately, all-glass bakeware manufactured and sold in the United States is tempered glass.

The tempering procedure substantially aids the structural stability of the glass vessel. And if it does break over time due to wear and tear, the tempered glass will shatter into little fragments rather than glass shards.

The different types of glass

1. Natural Glass

Microwaving natural glass cookware is generally safe. Dishes and mugs constructed of thick glass are safe to use. The heat will have little effect on the glass. Furthermore, you can safely use the thick casserole dish you got for Christmas in the microwave.

2. Synthetic Glass

Synthetic glass is a type of glass created in laboratories to meet industry specifications. Extreme temperatures and hazardous substances are frequently encountered in these industries. As a result, a material strong enough to store nuclear waste can withstand microwave oven radiation.

The following are two forms of synthetic glass that are used to make the best glassware for home and industrial use:

  1. Borosilicate Glass: A form of synthetic glass that contains around 15% boron trioxide. This chemical molecule is responsible for the thermal shock resistance of glass. Unlike conventional glass, borosilicate glass will not break when subjected to extreme temperature changes. As a result, borosilicate glassware may be removed from the freezer and placed on an oven rack without fracturing.
  2. Soda-lime Glass: This is the less expensive and more easily obtainable synthetic glass. Furthermore, it accounts for 90% of the world’s supply of manufactured glass. Soda-lime glass can be used for a variety of purposes. These goods range from furniture to wine glasses to elegant flower arrangements to windows.

Although it is relatively durable at normal temperatures, it is not as resistant to temperature changes as borosilicate glass. Soda-lime glass grows more than twice as fast when exposed to high temperatures. As a result, it will break more easily than borosilicate glass.

PYREX® Vs. Pyrex® – Is There a Difference?

You may be wondering where Pyrex comes into play.

PYREX® is a manufactured glass trademark that has been present in American markets since 1915. The long history of the PYREX® brand has earned it well-deserved respect. It has also become a household name in terms of cooking or baking.

PYREX® and borosilicate glass are words that have been used interchangeably. The rationale was that both represented the quality and durability of manufactured glass. Today’s Pyrex products, however, are not manufactured entirely of borosilicate glass.

Corning Glass Works has licensed the Pyrex brand to two separate firms. One manufactures only borosilicate glass PYREX®, whereas the other uses soda-lime glass to make pyrex® items.

Is Pyrex glass microwave safe? 

Pyrex glassware is popular in many households due to its ability to withstand microwaves and ovens. So, sure, Pyrex is microwave safe but always use caution.

Here’s how to find out:

  • American-made Soda-lime glass is used to make pyrex®.
  • However, French-made PYREX® continues to be made of borosilicate glass.

Examine the Pyrex product’s logo before purchasing it. If it has the upper case lettering PYREX, you know it’s the safer borosilicate glass. It could be from France or an old Corning Glass Works product from the past.

Vintage Corning Glass Works Pyrex items and contemporary French-made PYREX® are far safer in microwave ovens than American-made pyrex®. However, it is best to read the fine print when purchasing or using glass containers for cooking.

Pyrex items have been reported to fracture in high temperatures. As a result, when using Pyrex cookware and bakeware, keep the information above in mind to guarantee personal safety.

Injury risks when using microwave ovens

In terms of injury hazards, the United States Food and Drug Administration (USFDA) reports that most microwave-related injuries are heat-related burns. These burns are caused by hot containers that have been mishandled, exploding liquids, or overheated foods.

The majority of these injuries are unrelated to the radiation emitted by microwave ovens. That isn’t to suggest there haven’t been some. However, radiation injuries caused by faulty servicing or other unexpected circumstances are extremely rare.

Cautionary tips for using microwave ovens

Microwave ovens are frequently overly convenient for both household and industrial applications. As a result, consumers frequently overlook safety precautions when using microwave ovens. Here are some helpful hints from the USFDA:

1. Read and follow the manufacturer’s usage manual

The user manual lists all safety considerations and suggested operating practices. Among these safeguards are:

  • Liquids should not be heated for longer than the manufacturer’s recommended time.
  • When the microwave oven is empty, do not turn it on.

2. Use only microwave oven-safe containers

Is it safe to microwave glass? Glass cookware, such as borosilicate glassware mentioned in this post, can be used in the microwave. However, certain containers, such as metal pans and aluminum foil, must be avoided since microwaves reflect off them. As a result, it can harm both the food and the oven.

Furthermore, you cannot simply use any sort of plastic container in the microwave since heated food or liquid can cause it to melt. Therefore, only glass, ceramic, and plastic containers labeled microwave oven safe’ are recommended by the USFDA.

3. Avoid ‘super-heated’ water

‘Super-heated’ water is already over its boiling point but shows no apparent evidence of boiling. However, there have been reports of people using microwave ovens to heat water in a clean cup past the boiling point. As a result, it bursts violently with the least disturbance in the water. Severe skin burns and scorching injuries to hands and even faces are common complaints about this type of occurrence.

4. Periodically check for any leakage

The FDA advises inspecting your microwave oven for any damage to the door hinges, including seals and latches. Any of these problems can lead to excessive microwave radiation leakage. Under no circumstances should a microwave oven be used if the door does not appear to close securely. Avoid using your microwave if the door is deformed or bent, or is otherwise damaged.

5. Never use microwave ovens that work with open

Over the years, the USFDA has received several reports regarding microwave ovens that appear to stay on and continue functioning even when the door is left open. Radiation cannot be seen with the naked eye. As a result, we can never be sure that the magnetron is still producing microwaves in this state.

With this disease, it is advised to avoid using microwave ovens. Instead, notify the manufacturer right away.

Tips from USFDA 

Using glass can make working in the kitchen easier and less stressful. However, you must still take steps to avoid any annoyance or injury. According to the USFDA, microwave radiation injuries are uncommon but not unheard of. In addition, injuries caused by mishandling hot food or malfunctioning equipment are also highly prevalent.

To address these concerns, the USFDA has issued the following warnings against using microwave ovens:

  1. First, always follow the manufacturer’s directions.
  2. Only microwave-safe containers, such as borosilicate glass bakeware, should be used.
  3. ‘Super-heated’ water should be avoided.
  4. Check your microwave for leaks regularly.
  5. Finally, never, ever use microwave ovens with the door open.

The USFDA ensures that every microwave oven on the market meets a set of public-safe requirements. If your existing product is damaged, notify the manufacturer right away.

Microwave oven safety is certified by governmental authorities such as the USFDA. However, it is still up to customers like us to exercise extreme caution when employing this technology. Here are a few more tips for operating your microwave oven correctly:

  • Allow frozen foods to thaw at room temperature thoroughly. This should be done before placing food in the microwave to reheat.
  • Don’t you have time? To help the food thaw, use the low power setting on your microwave.
  • When handling glassware that has been heated in the oven, use pot holders.

General safety tips 

You now understand how to use your microwave oven correctly. Next, consider the following tips for utilizing glassware as microwave containers for reheating or cooking food:

  • Allow frozen food to thaw before reheating it in a glass container thoroughly. Also, before microwaving, wipe any condensation from the glass pan.
  • Another alternative is to place the frozen container in the microwave and slowly defrost it on low power.
  • When removing glassware from the microwave, remember to use potholders. Always use potholders, especially when handling food that has been heated for an extended period. You will avoid burn injuries due to heat transference if you use them.

Can you microwave cold glass?

Even though glass is generally microwave safe, microwaving cold glass is not an option. The chilled glass will crack or shatter when exposed to extreme temperature changes in a high-heat microwave.

Natural and synthetic glass containers that are room temperature or slightly chilly (recently chilled) are fine for microwave use, as long as the glass is tempered before heating.

If you are short on time and cannot wait for your chilled glass dish to warm up, it is preferable to use microwave-safe glassware. They are heat resistant and chemically inert, which means they will not react with your food.

Tips to microwave cold glass

You should know several things if you have a somewhat cold microwave-safe glass dish that you need to put in the oven.

When the glass container is removed from the refrigerator, condensation will form on its surface. Therefore, you are strongly advised to wipe away any condensation before placing the glassware in the oven.

If the cold glass container is not microwave-safe, run it for a few minutes in the microwave. After a few minutes, check on the food to determine if it is hot enough for you.

If not, give the dish a thorough swirl to break up the pockets of hot and cold. After that, return it to the oven for a few more minutes.

In this manner, even if your dish is not microwave-safe, you can be sure that it will not fracture.

What if there are no labels?

If the glass is simply unlabeled, you’ve discarded the product packing, or the bottom label has been wiped away due to wear and tear, you might conduct a brief experiment to see if it’s safe to microwave.

Please remember that if your glassware is tinted, has metallic or foil trim, or you know it’s glass-ceramic, you should not perform this test. This test aims to avoid breaking the glass in the microwave, not to look for additives, colors, or other contaminants.

Materials Needed:

  • GLASSWARE A: Glassware that you are trying to test. 
  • CUP B: A cup that you know is Microwave-Safe
  • Water
  • Microwave


  1. Check to see if GLASSWARE A has any labels.
  2. Set your microwave to the highest possible setting. This is accessible via power, power level, menu, or settings.
  3. 1 cup of water should be placed in CUP B.
  4. GLASSWARE A should remain empty.
  5. Microwave CUP B and GLASSWARE A together for 30 seconds. (Note: If GLASSWARE A is large enough to take up most of the area in the microwave, simply insert CUP B inside of GLASSWARE A. Pour no more water into GLASSWARE A.)
  6. For 1 minute, microwave CUP B (with water inside) and GLASSWARE A (empty).
  7. Touch GLASSWARE A carefully to feel how hot it is.

If GLASSWARE A becomes heated, it indicates that the material is unsuitable for microwave use. Most microwave-safe glasses will be only slightly warm to the touch. If the glassware is chilly and the cup of water is hot, the glassware is generally microwave safe.

Please remember that if CUP B was placed within GLASSWARE A, the area where the components were in contact with each other might have become heated. However, if the whole surface of GLASSWARE A is cool to the touch, it is probably safe to microwave.


So, to summarize, Can you put glass in the microwave? It is pretty easy to answer a seemingly simple question with a loud ‘yes.’ But, as we’ve seen, there’s more to it than meets the eye.

However, glass is a better alternative for microwave use than ordinary plastic containers. And it’s only natural to consider what kind of glass you can use. Microwave ovens produce radiation to cook food. As a result, utilize containers that can withstand radiation and significant temperature changes.

  • Natural Glass: This glass is similar to ceramic in that it may be used in the microwave. The greatest natural glass options are thick glass bowls and glasses. Why? Because temperature variations have little influence on the glass itself.
  • Synthetic glass: borosilicate glass is the finest choice for trustworthy, durable, and thermal shock-resistant glassware. The preferable option is PYREX®, which is made in France. Some Pyrex-branded items are already made of soda-lime glass. Unfortunately, soda lime is unable to sustain high pressure. As a result, it may shatter in the microwave.


Does glass melt in the microwave?

The glass becomes molten at temperatures ranging from 900°F to 1600°F, depending on the type of glass being manufactured. Standard microwaves cannot produce that much heat in any amount of time.

Because the microscopic air bubbles trapped in a glass container may shatter, crack, or explode. On the other hand, a microwave will not be able to melt glass.

As a result, you can microwave cold glass containers (microwave-safe) for as long as you need without worrying about melted glass.

Can you microwave crystal?

Crystal and glass are both remarkably similar. Is it possible to microwave crystal as well? This is not a good idea, especially with older crystal dishes. Even though the crystal is clear, like glass, it contains lead. This renders your crystal plates microwave-safe.

Can you microwave glass cups?

So we know not to put our beautiful crystal glasses in the microwave, but what about the glass ones? Can glass cups be microwaved? Not all glass is meant to be microwaved. If the wrong kind is used, it could break. Can you imagine a glass shattered with hot liquid inside?

That doesn’t sound like much fun. This is why, before putting your glass in the microwave, look for a microwave-safe label. If it does not have a label suggesting that it can be microwaved, it is better not to use it because there may be microscopic air bubbles in the glass cup. When heated, these bubbles expand and shatter if they expand too much.

Are glass bowls microwave safe?

Microwaves heat food by emitting radiation waves, which first interact with the water in the meal. If you’re thawing something in the microwave, use low power until all of the frosts have been removed from the meal, then stir and integrate the hot and cold as best you can.

Although tempered glass cookware, it can still break when subjected to high temperatures. If you cook something so that half of your dish is frozen and part of it is boiling, you may end up with a potentially deadly mess on your hands. ​