What is the microwave safe symbol? (Signs Included)

While microwaving is very convenient and easy, at times, it can be confusing. Especially if you don’t know whether the plastic containers you want to heat up are microwave-safe or not. 

Will it cause an explosion? Can microwave safe containers leach potentially dangerous chemicals into your food? Should you even put it in the microwave in the first place?

The answers to all these questions come down to one thing: the microwave-safe symbol. 

What is it, and what does it really mean? I answer all that and more in this article.  

What is the microwave-safe symbol?

microwave safe plastic symbol


The microwave-safe symbol is simply a microwave with three wavy lines, which is usually found on containers made to use in a microwave. There are three versions of it typically used on different containers, the first is a plate or circular surface with three waves. The second one is a microwave with the same 3 wavy lines inside.

The last one is recycling #5, usually present in plastic containers.

Sometimes, it can be tricky to understand which symbols on a plastic container mean it is safe to put in the microwave. You might even question if you should put it in the microwave or not. This is where a microwave-safe symbol or label comes in handy. These labels and symbols mean that the container has been tested by experts. They also mean that the box meets industry standards.

So, what is it? 

The main thing you need to look out for is three wavy or squiggly lines that represent radiation waves. These lines can either be drawn on top of a dish or inside a microwave. So, if those three lines are present, you can go ahead and reheat food in those types of plastic containers.

If the container doesn’t have any symbols drawn on it, it might have some text to help you identify if it’s microwave-safe or not. Usually, you can find words like safe for microwave use or microwave safe written on the bottom. 

In the case of plastic containers, you might not find the microwave-safe symbol or even phrases. Instead, you’ll usually find a recycling number or resin ID code that indicates the kind of plastic container. 

What does the microwave safe sign mean?

microwave safe plastic symbol

The microwave-safe symbol is all about the temperature. It basically means that the material used to make the plastic containers won’t directly melt under microwave heat. This is possible because of the way a microwave heats up the food.

A microwave works by heating water molecules such that they start to vibrate and generate heat as a result of the friction. This means that if there’s no water, no heat will be generated. This also means that a microwave-safe container contains only a small amount of water. As a result, the dish won’t heat up, and the microwave’s heat is directed toward the food. 

Non-microwave-safe plates, containers, bowls, and cups might contain materials like plastic or metal that aren’t entirely microwaveable. Meanwhile, ceramic, glass, and borosilicate pots are microwaveable. 

If you’re interested in more on what it means, click here.

How to tell if something is microwave-safe

You can easily tell if something is microwave-safe by looking for microwave safe symbols or words like CPET. Similarly, words like APET, Styrofoam, and PS mean that the containers are not microwave-safe. If you can’t find any of these, you can do a quick test to check if the container is ok for microwave use. Fill the container with roughly 250 ml of cold water and heat it on high power for a minute. If the plastic container is warm, it’s not safe to put in the microwave. But if it’s cold, then it’s most probably microwave-safe.  

First, look for the microwave-safe symbol at the bottom of the dish or plastic packaging. If there’s no symbol, but you find #05 and PP on it, that means the container is made of polypropylene and is safe for microwave use. Similarly, containers saying #1 and CPET are safe to put in the microwave since they can tolerate higher temperatures.   

Meanwhile, containers made of APET(E), #1 aren’t safe to put in the microwave. These are usually water bottles, supermarket containers, deli containers, or any other container used to display cold foods. While they are recyclable, they shouldn’t be subjected to heat. 

Styrofoam, #7, and polystyrene aren’t microwave-safe either. Most clamshells and takeout containers are made of foam because of how well it retains heat. But they’re not safe for heating either. 

The same goes for harvest fiber and paper products, especially since the latter is often glued, sealed, or coated. Heating them could result in harmful chemicals leaching into your food.    

What is a non-microwave-safe symbol?

The non-microwave-safe symbol is essentially a microwave-safe symbol but with a line diagonally cutting through the center. 

Just like there are microwave safe symbols, there’s also a non-microwave-safe symbol. In most cases, it’s just a microwave with three squiggly lines but with a diagonal line running across the whole thing. In other cases, the symbol is accompanied by a text saying “Do not microwave.” 

Which food containers are safe for the microwave?

symbol for microwave safe

Generally, ceramic, glass, and some kinds of plastics are considered microwave-safe. Meanwhile, soft plastic, metal, and wood are not microwave-safe.

It might come as a surprise, but you can microwave flat aluminum foil that has sharp corners. This kind of foil doesn’t trap microwave radiation, so the risk of fire is low. In fact, many people use some foil to cover things they don’t want to overcook in the microwave. Just make sure that it doesn’t touch the microwave wall; otherwise, it can result in arcing.

Dinnerware is also safe to microwave as long as it is not cracked or chipped. In most cases, you’ll find a microwave-safe label underneath plates, cups, and bowls.

Glass jars are also okay to microwave as long as you remove the lid, especially if it’s made of metal. Just be careful not to heat it for too long; otherwise, it will break. Similarly, only use heat-resistant glass but make sure it isn’t cracked or chipped or contains any metal parts. Also, avoid microwaving cold glass as soon as you pull it out of the refrigerator since it can break.

Microwave cooking bags are also, well, microwave-safe but just make sure you follow the manufacturer’s instructions when nuking them. Make sure you make some slits in the bag so that there’s some room for steam to escape. And while most microwave bags come with a metal tie in the package, never use them in the microwave; they’re for the oven.  

And, of course, then you have plastic packaging. Some kinds are meant to reheat food but make sure you check for the microwave-safe symbol or label. Most popular manufacturers like Ziploc, Tupperware, and GladWare design microwave-safe plastic containers. But some companies produce food safe containers that soften when put in the microwave. 

And finally, you can also use cling wrap/plastic wraps in the microwave as long as they are labeled safe. Just make sure you don’t let the plastic wraps touch the food otherwise, it can leach harmful chemicals into the food. Also, leave some space for the steam to escape to avoid the chance of an explosion. 

What materials are not considered microwave-safe?

microwavable plastic containers

Things like metal twist ties, food cartons, wood, paper bags, aluminum trays, and metal utensils are not safe to microwave.

Metals like metal twist ties, aluminum trays, and utensils can cause arcing. The same goes for food cartons that contain some kind of metal, like metal handles in Chinese takeout boxes. Metal utensils can also prevent microwave radiation from reaching the food. 

Paper bags can also cause a fire, while wood can dry up, split, or crack.

The Bottom Line

You now know what the microwave safe symbols are and even what the non-microwave-safe symbol looks like. And you’ll most likely find either the symbol or a label present at the bottom of the container. This way, you can easily determine what to put and what not to put in the microwave. 

Remember, some hard plastics, ceramics, and glass are safe to microwave. Meanwhile, you shouldn’t put metals, wood, and soft plastic in the microwave. 


How can I tell if a dish is dishwasher safe?

Dishwasher safe dishes will typically have a symbol of a square box with glass, plates or utensils in it. It is also usually written on the packaging of the dish or on the bottom of the dish itself.

How can using microwave safe containers help combat food waste?

Microwave safe containers, such as tupperware, allow for easy reheating of leftovers, keeping them fresher for longer. This can reduce the amount of food wasted, as people are more likely to save and reheat leftovers if they can do so easily and safely.

What should I consider when using glass containers in the microwave?

Glass containers that are labeled as microwave safe will typically have the microwave safe symbol on them, but you should also check to make sure they can withstand the microwave temperatures. Avoid using glass containers that have metal parts or decorations, as these can cause sparks and damage to your microwave.

How important is it to use microwave safe containers for food storage?

Using microwave safe containers for food storage is important to ensure that your food is kept safe and free from harmful chemicals. It also allows for easy reheating of leftovers, which can help combat food waste.

How does microwave heating affect the safety of plastic containers?

Microwave heating can cause plastic containers to break down and release harmful chemicals into your food. This is why it is important to use microwave safe plastic containers, which are designed to withstand the temperatures and energy of a microwave oven.

Are tupperware containers freezer safe?

Many tupperware containers are freezer safe, but it is best to check the packaging or the container itself for a freezer safe symbol, or to check with the manufacturer.

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