Is it Safe to Put Cardboard Into Your Microwave Without Catching Fire?

Are you getting takeout tonight ordering a pizza for delivery? When you’re ready to reheat those leftovers, can you safely reheat them in cardboard?

Should you transfer your food to a traditional plate or bowl before you microwave, or is cardboard safe?

The short answer to this question is both yes and no. You can microwave cardboard, but there is an inherent danger that happens when your cardboard’s exterior coating or the inside of the cardboard gets heated.

This can cross-contaminate your food with chemicals, and it’s also possible for cardboard to ignite when you expose it to extremely high temperatures. However, this is unlikely to happen in the microwave.

Since most fast-food restaurants pack and deliver their food in cardboard containers.

For example, if you’ve ever ordered Chinese food or a pizza, you’ll get cardboard to-go containers delivered to your house.

If you’re not sure about whether or not you should reheat the food in these containers or transfer it to something else, read on.

Is it Safe for You to Microwave Cardboard?

The answer to this question isn’t straightforward because if your container is made up of pure cardboard, you can easily microwave it without causing damage to your food, microwave, or to the container.

However, there are some types of cardboard that won’t do well if you microwave them.

Cardboard containers can have plastic, wax metal, ink, or glue in their makeup as a coating, either layered between the corrugated material or on the outside of the box.

Always read the label so you can know whether or not your type of cardboard can go into the microwave for you to reheat your food. Whatever the case may be, you should never overheat your cardboard container.

Additionally, cardboard containers can have chemicals that can be hazardous when you heat them up in the microwave, and these compounds can leach into your food and make it unsafe for you to eat.

So, if you’re wondering if you can microwave your specific container, read the label.

If the manufacturer tests the container to see whether or not it’s safe to put in the microwave, they’ll tag and label it as microwave-safe.

If the cardboard container isn’t safe to microwave, it could have a disclaimer on it instead. Carefully check for any labels and read the manufacturer’s instructions before you heat it up.

Can Cardboard Catch on Fire in the Microwave?

When you consider the fact that cardboard is a conductor of fire, it makes sense that you would think that it would quickly catch on fire very quickly when you expose it to heat.

However, this isn’t necessarily true, depending on the type of cardboard you want to try and microwave.

Corrugated cardboard or cardboard that features a combustible material can catch on fire if you expose it to an open flame or sparks.

Additionally, your cardboard can spontaneously combust if you manage to heat it to temperatures of 800-degrees Fahrenheit.

However, since most home appliances function the same way, it won’t be a large concern for you under any circumstances.

Generally speaking, cardboard boxes that are made out of pure wood pulp or fiber without any additional materials are safe to microwave without worrying about them catching on fire.

However, a lot of cardboard boxes can have tiny metal elements that keep the different pieces together, or they can have a thin coating of plastic inside them to prevent food or grease from leaking through.

In these cases, heating up your cardboard in the microwave can be a dangerous thing to do.

Also, you don’t want to microwave your cardboard for an extended period of time. Prolonged heating of your cardboard can increase your chances of having a fire due to it overheating.

If your cardboard is made out of wood fiber like paper, it’ll generally have a 9% to 12% moisture level in it. The moisture levels will start to drop as it heats up.

Once the moisture content of this cardboard drops below 1%, the fibers completely dry out. This can result in them catching fire due to spontaneously combusting. So, microwaving cardboard for a long time will eventually cause a fire.

This process slows down a lot when there are beverages or food in your microwave.

Generally speaking, microwave energy gets absorbed by the water molecules, sugar, and oil inside the food or drinks.

Tips for Microwaving Cardboard

Always read and follow any manufacturer instructions on your cardboard before you attempt to reheat it, even if you think that it’s safe to do so.

They’ll usually put these instructions clearly on the box or container, so they’re easy to see at a glance to avoid fires or other issues with people accidentally microwaving non-microwave-safe cardboard.

When you microwave your cardboard, you should always do so in short bursts. It can be safe to microwave any cardboard with a microwave-safe label, and it’s very unlikely to catch fire, stick to 30-second intervals.

Take the cardboard and food out and check them before continuing to heat them.

If you just allow your cardboard to microwave for long periods of time, you risk drying it out and making it more prone to catch fire.

Also, ensure that there is no wax or plastic coating on the food that can leach into it as it heats up.

Many companies put this coating on their cardboard to make it resistant to leaking when they put the food in it.

It’s also a good idea to remove metal, plastic, or paper pieces from the cardboard before you microwave it.

So, you may have to remove any plastic lids on disposable coffee cups; a metal clip used to securely close the box, or a plastic pizza box holder before you microwave it. Metal will spark and short out your microwave if you don’t catch it right away.

Hot Long You Can Microwave Cardboard

As we touched on briefly, you should never microwave your cardboard for extended periods at one time.

Instead, you can microwave it anywhere from 30 to 120 seconds at the most. If you want to microwave your cardboard for a longer period, you should do so in shorter intervals before you stop and restart the heating process. This will allow the cardboard to cool down minutely each time you take it out.

That being said, you never want to go over 120 seconds without stopping the microwave.

It’s true that you can heat foods up faster when you do so on cardboard, but tea or coffee most likely won’t heat up as quickly. Cardboard beverage containers can take a longer duration to heat up completely.

When you heat up beverages, you do want to stop every 30 seconds and stir them to prevent them from superheating since the containers have a completely smooth surface.

Superheated water or liquid has a much higher chance of exploding and causing burns because they don’t create bubbles as it heats.

Also, the liquids tend to heat unevenly in the microwave, and stirring them will help distribute the heat more evenly each time you stop the microwave.

Bottom Line

You now know that it is and isn’t safe to put cardboard in the microwave, depending on the type of cardboard you use and whether or not it has a wax or plastic coating on the interior.

If you choose to heat the cardboard, pay attention to the manufacturer’s warnings and heat it in slow intervals.