Use paper plates instead of regular plates, reheat your pizza in its box, or microwave leftovers in their cardboard takeout containers to make things more convenient. Can cardboard be safely microwaved, though?

You can microwave cardboard that is made entirely of cellulose for brief intervals if it is microwave-safe.

Continue reading to learn why some cardboard can be safely microwaved, what cardboard shouldn’t be microwaved, and how to microwave cardboard safely.

Is It Safe to Microwave Cardboard?

You can microwave cardboard that has been treated for use in the microwave for a brief period of time if it is made entirely of cellulose. Simply keep it between 60 and 120 seconds, checking every 30 seconds to lower the chance of overheating the cardboard. Keep your microwave on a low power setting, too.

Transferring the food to another microwave-safe container is a better option if you need to heat something for a longer period of time. Why? Because cardboard is flammable, especially at temperatures of over 400°F or for prolonged periods of time—this causes the moisture level in the cardboard to drop, making it more likely to catch on fire.

Read More: How Does A Microwave Oven Work – Complete Guide to Use It in 2023

How Does Microwave Warm Up Cardboard?

We must first comprehend what exactly occurs inside the microwave in order to understand how it affects cardboard. Microwaves are produced in a microwave oven to operate. Sure, but what exactly are microwaves?

With a wavelength in between radio waves and infrared light, microwaves are electromagnetic waves. A magnetron vacuum tube that is incorporated into every microwave oven produces microwaves at a frequency of 2450 MHz.

How do microwaves heat your food? Water, fat, and sugar molecules take them up as a result of which these molecules begin to rotate and engage in interactions with other molecules. Your food, drink, and cardboard will become warmer as a result of this molecular dance, which produces heat.

You should only use certified plastic containers in your microwave because some types of plastic can absorb microwaves.

How Does Cardboard Interact With Microwaves?

There are many existing types of cardboard, such as corrugated or triple wall cardboard. They all share one thing in common, though: they are all made of cellulose, the wood fiber found in paper.

The typical moisture content of cardboard is between 9 and 12%. The moisture content will start to drop if you microwave it, and depending on how long you microwave it for and how much surface area it has, it could even drop to 1%.

If you leave the microwave on, the cardboard is likely to dry out completely and catch fire because this process can sometimes happen quite quickly. Keep in mind that this scenario only applies when you put cardboard in the microwave by itself, without any other items (such as food or drink).

As a result, avoid microwaving cardboard by itself since it could catch fire in some circumstances. Anything made of cardboard has the potential to catch fire.

I’m aware that there are some comments and articles that say it’s acceptable to microwave cardboard even on its own (for drying purposes, for example), but I want to draw your attention to the fact that if it’s not done with great care, it can be seriously dangerous. Although it is true that a lot depends on the kind of cardboard you use, I do not advise simply microwaving cardboard by itself.

Can a Pizza Box Go in the Microwave?

As long as you can find a microwave-safe label or written instructions, you can usually microwave pizza boxes without incident. While many brands produce reheat-safe boxes, some may also contain plastic or metal. Make sure the box is in the microwave for less than a minute.

What About Cardboard Boxes and Containers With Food Or Drink?

Now that we’ve established that it’s not a good idea to microwave cardboard on its own, let’s look at the situations in which you simply want to reheat food or beverages in a cardboard container.

As I’ve already mentioned, there are many types of cardboard containers. Until there is food or liquid inside, cardboard boxes that only contain wood fiber are typically safe to microwave.

Since the water, sugar, and oil molecules in the food are the main things that are heated in a microwave when you reheat food or beverages in a cardboard container, the moisture content of the cardboard won’t drop to a risky level.

Therefore, it’s usually safe to warm up food and drink in a container made of pure cardboard under supervision (unless the label says otherwise). Of course, you shouldn’t cook or boil in these containers, but most of the time, reheating is acceptable. In fact, overheating food in a cardboard box in the microwave can harm both the container and the food inside.

Types of Cardboard You Can’t Microwave

Here are the common cardboard containers you should not microwave:

• cardboard that has been adhered with glue or another adhesive. This can release chemicals into your food.
• In addition, printed-on cardboard can release chemicals into your food.
• lining-lined cardboard. Wax and plastic linings can release chemicals and fumes into your food (here’s more about whether you can microwave plastic).
• Hello, Chinese takeout. Containers with metal handles. In a microwave, avoid using metal.

Here’s the scoop on how to microwave glass and whether or not you can microwave paper plates.

Will Cardboard Light on Fire in the Microwave?

You’ve come to the right place if you’re uncertain about whether or not cardboard can catch fire in a microwave. Cardboard is a quick fire conductor, so it can spread quickly if it is exposed to flames.

When exposed to sparks or an open flame, cardboard or corrugated board can catch fire. Furthermore, at a temperature of 427°C, cardboard can spontaneously ignite.

However, due to the way that home appliance microwaves work, it won’t be a significant issue most of the time. In general, cardboard boxes made entirely of wood fiber or pulp without the addition of any other materials can be microwaved without issue.

However, cardboard boxes may have small metal elements that help to keep the pieces together or can have a thin coating of plastic liner to prevent leaks and waterproof the surface. Microwaving cardboard in these circumstances can be risky.

Additionally, be careful not to microwave the cardboard for an extended period of time. Prolonged heating can increase the chance to catch on the fire due to overheating.

The cardboards are made from wood fiber i.e. cellulose like that of the paper, which generally contains a moisture level of 9 to 12%. This moisture level will begin to decrease as you microwave the cardboard.

Once it drops to 1% or below, the fibers will get completely dry, which can result in catching fire due to spontaneous combustion. Hence, microwaving cardboard for a very long time can result in fire.

If there is food or drink in the cardboard, this process is noticeably slowed down. Generally speaking, the food or beverage’s water, oil, and sugar molecules are the main absorbers of microwave energy.

How Long Can You Microwave Cardboard?

Cardboards shouldn’t be microwaved for an extended period of time, as was previously mentioned. It can be heated in the microwave for no longer than 120 seconds.

It is preferable to stop the heating process for a brief interval of 30 or 60 seconds before starting it up again if you want to microwave cardboard for a longer period of time.

That being said, you should not exceed 120 seconds in one go. Though foods can be heated up faster when nuked on a cardboard surface, coffee or tea may not be heated up so fast. It might take longer to heat up cardboard beverage containers.

Tips to Microwave Cardboard

Microwaving cardboard does present some risks in regards to overheating resulting in spontaneous combustion, plastic or metal parts, or cross contamination from leached chemicals on the surface.

Here are some tips for you to microwave cardboard:

1. Be sure to read the label before putting cardboard in the microwave. If the product has undergone testing, the manufacturer will indicate it on the packaging. In the absence of that, eating food or even heating cardboard can be quite risky for you.
2. Check to see if the cardboard is waxed or has a plastic coating because these two materials can be dangerous when exposed to the heat produced by a microwave.
3. The cardboard should be microwaved for only a few seconds, i.e. 60 to 90 seconds for most of the cases. Drinks or beverages that are liquid can be nuked for 120 seconds.
4. Before you microwave the cardboard, remove any paper, plastic, or metal pieces. Remove the plastic lid from disposable coffee cups, the pizza box holder made of plastic, or the metal clip that holds the lid in place before placing it in the microwave, for instance.

Microwaving Cardboard: Final Summary

It is evident from the above explanation that before microwaving cardboard, you must make sure to read the manufacturer’s instructions on the label. Otherwise, it is better to transfer the food or beverages to a microwave-safe cup, bowl or plate to reheat. Both for your own personal consumption and the microwave’s safety, it is better.

In general, you can use cardboard that is microwave-safe to heat food. If the cardboard is pure fiber or cellulose material, then there should be very little concern about hazards.

Check the following guides to learn what kind of materials can be put in the microwave!