How to Tell if Something is Microwave Safe?
What to know

How to Tell if Something is Microwave Safe? (Answered)

On one hand, many plates and bowls offer microwave-safe features. On the other hand, by using the wrong dish, you could end up ruining both your dinner and the dinnerware itself. Microwaves provide convenience to those who use them.

Regardless, you should observe several precautions when microwaving dishes. For instance, you should test whether a dish is fully microwave-safe or partially microwave-safe. Does it warm up a little when you microwave food on it? Or do the microwave rays not affect it at all?

Helpful Microwave-Safe Labels

Check the dish if it sports the microwave-safe label and logo. This means the Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA) considers it safe for use inside the microwave without fear of breakage from thermal shock or becoming flammable.

The heat tolerance of glass and ceramic makes microwave-safe labels less of a concern for them. Better to err on the side of caution, though. In regards to plastic, certain plastics melt easily or could catch fire when heating them up long with food. However, the likelier scenario involves leaching BPA.

The label tends to be an icon of a microwave with wavy lines on it. It might also contain the text “microwave-safe” for good measure.

How to tell if a bowl is microwave safe?

In order to tell if a bowl is microwave-safe, microwave a cup of water with a dish for a minute. If the container or dish ends up hot or warm after microwaving then it’s not microwave-safe. If the dish or container remains cool while the cup of water got hot, then it’s microwave-safe.

Some microwave-unsafe containers can scald, melt, or break. Thermal shock could happen on thin glass containers that offers little to no heat-resistance.

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The Issue with Metal Containers

Other containers cold damage the interior of the microwave, particularly the ones made of metal. Foil-lined containers, aluminum wraps, or metal trays could all cause a phenomenon known as electrical arcing.

The electricity could cause sparks to form or burn the food being microwaved. It could also superheat the metal. Use microwave-unsafe containers for serving food or storing food. Never use them to microwave your leftovers or dishes.

How to know if plastic is microwave safe?

Look for the microwave-safe mark on plastic containers and plastic wrap. The label signifies that the FDA itself views such products as BPA-free. They won’t leach off plasticizers and other chemicals into your food when heated. However, don’t put plastic wrap in direct contact with food regardless.

Just use them to seal the top of the container as a lid of sorts. Poke holes in them for pressure release. Don’t use any container with cracks or damage on it even if they’re reusable. They’ve been compromised for microwave use.

What is BPA? Why Should Microwaveable Plastic Be BPA-Free?

A microwave-unsafe plastic container tends to leach of BPA or Bisphenol A. This plasticizer makes plastics hard. It could also leach off of certain plastic containers when heated.

A labeled reusable microwave-safe plastic container should be transparent to the microwave radiation while at the same time has enough heat resistance to deal with the hotness of the food.

How to tell if Styrofoam is microwave safe?

For the most part, don’t microwave Styrofoam or polystyrene foam. They tend to lack microwave radiation resistance. They could catch fire and melt when microwaved. Some Styrofoam cups can resist even the hottest of coffee liquids.

Even those foam cups should not be microwaved unless they have the microwave-safe label printed on top or below them. With that said, yes, you can microwave any Styrofoam container that contains the microwave-safe label and logo. Just like plastic.

Styrofoam Can Be Microwaveable

Yes, you can microwave Styrofoam with the proper marking. However, fewer people use them for microwaving. Many err on the side of caution and transfer food on microwavable bowls for microwaving purposes. Plastic seems more microwaveable than Styrofoam.

Speaking of which, microwaveable Styrofoam tends to contain PP or polypropylene, which is considered microwave-safe. The makers of ProView and Smart Set Pro Styrofoam containers made them with microwave use in mind.

styrofoam microwave
Styrofoam Microwave

How to tell if a mug is microwave safe?

Mugs composed of ceramic or thick glass tend to be microwave-safe. You can test them for microwave-safeness in case you’re not sure if they’re microwave-safe. As usual, put ice-cold water on it and microwave on high for about 4 minutes.

1-kilowatt microwaves tend to make the water boil in 1-2 minutes. 650-watt to 700-watt microwaves can boil the water within 3-4 minutes. Anything below that takes about 5 minutes or more. From there, touch the mug. If it’s cold but the water ends up hot then it’s microwave-safe.

Non-Microwaveable Mugs

If it’s warm while the water is hot then it’s only partially microwave-safe and should not be used for cooking just reheating. If it’s as hot as the water it’s absolutely not microwave-safe and should not be used for microwaving at all.

Even mugs made of ceramic, stoneware, earthenware, or glass could end up non-microwaveable because of low heat tolerance and increased thermal shock risk. Plastic mugs might be heat-proof but could melt or leach off BPA if microwaved. Wine glass cracks when heated.

How to tell if a fabric is microwave safe?

For the most part, don’t microwave fabrics. Microwave makers made their product for food reheating use. Many a fabric could also be fire risks or fire hazards when microwaved since water molecules aren’t the only molecules that get affected by microwave radiation.

Further reading: Is Glazed Cotton Thread Microwave-Safe?

Natural vs. Synthetic

If you’re into microwaving fabrics for heating pads or the like then the rule of thumb is natural is microwaveable. Cotton and wool fabric show more resistance against microwave exposure than plastic weaves and fabrics like rayon or synthetic and natural blends.

Synthetic fabrics tend to be especially prone to melting and getting set on fire due to heat. This is also the reason why many manufacturers avoid having such threads ironed out with an electric iron. They can be quite meltable to the point of damaging the inside of your microwave or burning your skin.

How to tell if Tupperware is microwave safe?

Manufacturers of microwave-safe Tupperware mark it as such. There should be a label of “microwave-safe” followed by 3 wavy lines signifying the microwaves themselves. Look at the bottom of your Tupperware or Rubbermaid brand container to ensure.

Any plastic container lacking such symbols and labels at the bottom should not be microwaved. Err on the side of caution. Even if they are microwave-safe you just can’t be sure because they lack the label and thusly the FDA approval for microwave use.

Further reading this post: Can You Microwave Tupperware? Learn More Here.

According to the WHO

According to the World Health Organization (WHO), it’s safe to microwave food in general. Only certain containers, however, have approval from the FDA and USDA for microwave use. If the Tupperware doesn’t have a microwave-safe label it shouldn’t be microwaved.

This is because microwaving plastic containers can result in leaching or the leakage of chemicals into food, contaminating them with plasticizers. BPA is a big one as well as phthalates. A BPA-free microwave-safe container is one that won’t melt when microwaved and won’t leach toxins into food.

How can you tell if a container or covering is microwave safe?

Check the bottom for the microwave-safe label and wording. It should have a microwave oven icon with wavy lines on it or just the wavy lines. The word “microwave-safe” is a good indicator of how microwaveable a given container is.

You’re less likely to see this in ceramics and glass containers but the best ones have that marking. Even then, you can err on the side of caution and test the items to see how microwaveable they really are. You can also play it on the safe side by not microwaving unmarked plastic and Styrofoam.

Microwaving Plastics and Leaching

Non-microwaveable plastic dishes could melt and contaminate the microwave interior. The melted plastic could also get set on fire, which produces far worse toxins (like carcinogens) than simple BPA and phthalates.

You can also test an item by microwaving an ice-cold glass beside or inside them for 2-4 minutes then checking if the item has become warm or hot like the water. If it truly is microwaveable, it should remain cold even as the water turns hot.

FAQs – Frequently Asked Questions:

Here are the most frequently asked questions regarding what’s microwave-safe or not.

What things cannot be put in the microwave?

Anything that isn’t food.

Paper bags, unlike paper plates, release toxins when microwaved and could even catch fire. Single-use takeout containers without microwave-safe marking shouldn’t be used as well.

Hardboiled eggs, Styrofoam and plastic storage containers with no microwave-safe marking, cookware with metal trim, sauce, or dip without cover, grapes, and peppers shouldn’t be microwaved either.

In the case of grapes, they explode and catch fire. In the case of pepper, they release capsacin that acts like eye-burning tear gas when you open the microwave door.

Some people microwave fabrics and other items with the intention of heating them up quickly for warmth, like in the case of heating pads or bags. Make sure the non-food item you’re heating up is microwave-safe though. Synthetic fabrics tend to catch fire in the microwave oven.

See more: What Are The Things You Should Never Put In The Microwave?

What can you put in a microwave?

Food for the most part. You can microwave ready-made dishes like leftovers from last night’s dinner just fine. Companies manufacture microwave ovens with cooking, reheating, or defrosting food items in mind.

What Can You Put in a Microwave

Microwave-safe containers mainly include paper plates without special plastic coating, plastic wraps like Saran wrap or Reynolds wrap (no contact with food please), plastic or Styrofoam containers with microwave-safe markings, and thick glass (not wine glass) and ceramic containers.

Certain food items like grapes and peppers shouldn’t be microwaved due to their effects on the microwave afterwards. Microwave any non-food items with due caution. The microwave oven isn’t designed for microwaving anything that isn’t food.

See more this post: What Can You Put in a Microwave?

What kind of metal can you put in a microwave?

Tin foil or aluminum should not be put inside a microwave. Many metals can cause arcing to occur when placed inside the microwave then bombarded with microwave radiation.

According to the USDA, aluminum foil can safely be microwaved in small quantities and as long as the foil is new and smooth instead of used and crumpled. The crumpled bits of foil can conduct electricity better, which results in the radiowaves turning into arcing sparks and bolts of electricity.

Containers for items like hot pockets are lined with aluminum and they could be microwaved fine without all those dangerous sparks and electric bolts. You have to be careful though and immediately turn the microwave off as soon as arcing occurs!

You may also like: What Happens When You Put Metal in a Microwave?

Is it dangerous to run an empty microwave?

Yes. Don’t do that. Something must be inside the oven while it’s turned on in order to catch all those microwave radiation or energy. Otherwise, the microwaves will bounce back to the unit itself, causing potential damage.

The food absorbs the microwaves normally. When there’s no food or beverage to absorb all that energy within the microwave interior, a large amount of energy ends up reflected around the chamber, which results in large standing waves that could overheat or destroy the device.

You don’t turn on your oven toaster with nothing inside. This goes double with running an empty microwave in light of the nature of microwave rays.

What More Can Be Said?

The FDA classifies most glass and ceramic cookware as microwave-safe as long as they don’t have silver or gold rims. Glass cups might or might not be microwave-safe. You should test the glass in order to see if it can stay cool after microwaving.

Don’t use frozen food containers and trays. The makers of these items designed them for one-time use instead of multiple uses. Don’t microwave butter tubs, whipped topping bowls, and other food containers. The microwave rays and high temperatures might induce them to release toxic chemicals.

For the same reason, don’t microwave any plastic containers not rated as microwave-safe or BPA-free. If the container got cracks or is old, don’t microwave it either. Only use undamaged containers because damaged ones can leach off plasticizers all over your food.


  1. Guide: How to Tell if Something is Microwave Safe“,, November 18, 2015

Through the years, the microwave oven has become a standard appliance for all homes. It is safe to say that there is no home without a microwave oven. If you are looking for a microwave oven that best fits your needs, You find the right website.

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