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Can You Microwave Cardboard?

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Are you ordering a delivery pizza or you’re opting for a takeout dinner tonight? When it comes time to reheat those leftovers, is it safe to microwave cardboard?

The answer is both yes and no. The inherent danger occurs when the exterior coating or inside of the cardboard is heated, which can potentially cross-contaminate food with potentially harmful chemicals.

Cardboard can suddenly ignite when exposed to extreme high heat, however that is very unlikely to happen in a residential microwave.

Well, most quick service restaurants pack and deliver foods in cardboard containers. If you are familiar with ordering takeout pizza or Chinese food, then you will often encounter cardboard to-go containers.

Sometimes these foods are not entirely finished, and you have leftovers. 

Reheating food in the microwave is a common practice, but do you need to dirty a dish or can you microwave food in the takeout box?

Therefore, the main question that is asked by most of the people is whether or not it is safe to microwave cardboard. If you choose to reheat the food right in takeout container, then you need to make sure it is safe to do so.

Is it safe to microwave cardboard?

A straight yes or no answer to this question is a bit complicating. If the container is made up of pure cardboard, then you can surely microwave it without causing any damage to the food, container or to the oven itself. 

However, some types of cardboard are not safe to be microwaved. Cardboard containers can contain wax, plastic, glue, ink or metal as a coating on the outside or layered in-between the corrugated material. 

Always read the label to know whether or not the cardboard can be put into a microwave oven for reheating the food. But in any case, you should not overheat a cardboard container.

Cardboard containers even contain chemicals that can be quite hazardous when heated in a microwave. The compounds can leach into the food and make it poisonous for you to ingest. 

So, if you are wondering if you can safely use the cardboard inside a microwave oven, then you will need to read the label. 

Cardboard containers will be tagged or labeled as microwave safe if they have been tested by the manufacturer. On the other hand, cardboard containers that are not safe may come with a disclaimer. 

Carefully read the manufacturers instructions, and check for any label on the cardboard!

Is it safe to microwave cardboard?

Will cardboard light on fire in the microwave?

If you are confused about whether the cardboard can light on fire in a microwave or not, then you are at the right place. Considering the fact that cardboard is a quick conductor of fire, it can easily catch fire. 

Corrugated board or cardboard is a combustible material that can catch fire when exposed to sparks or open flame. Furthermore, cardboard can spontaneously combust when heated to a temperature of 427°C.

However, the way that home appliance microwaves function, it will not be a major concern under ordinary circumstances. Generally, cardboard boxes made of pure wood fiber or pulp without any additional materials are usually safe to be microwaved. 

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. In such cases, heating cardboard in the microwave can be dangerous.

In addition, make sure that you do not 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%. When you microwave the cardboard, this moisture level will start to drop. 

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. 

This process is drastically slowed when there is food or drinks in the cardboard. In general, the microwave energy is mainly absorbed by water molecules, oil and sugar inside the food or beverages.

Can you microwave cardboard safely?

While cardboard is generally safe to be used in the microwave, it is always recommended to read the manufacturer instructions provided with the material. 

Sometimes when you opt for a takeout meal or pizza delivery at your home, reheating instructions will be clearly displayed directly on the container cardboard package. 

Do not use cardboard in the microwave oven unless the packaging is labeled as microwave safe. For instance, it is recommended to remove food from the pizza box and burger box to safely reheat leftovers.

When microwaving cardboard, make sure that you are heating it for short periods of time. Though it can be safe to use microwave safe cardboard, and it is also very unlikely to catch fire, it is better to stick to a shorter duration. 

Otherwise there is a chance the moisture level of the cardboard will drop leading to catch a fire. Stick with safe practices and you should be able to nuke microwave safe cardboard without any concerns.

How long can you microwave cardboard?

As mentioned above, cardboards should not be microwaved for extended lengths of time. You can microwave it for a shorter span like 60 seconds to 120 seconds at the most. 

If you want to microwave cardboard for more time, then it is better to take a short intervals for 30 seconds or a minute before restarting the heating process. 

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. Cardboard beverage containers may require longer durations to heat up.

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. Make sure to check the label before using cardboard in the microwave oven. The manufacturer will label the packaging if the material has been tested. Without that it can be quite dangerous for you to consume food or even heat the cardboard.
  2. Look if the cardboard is waxed or coated with a plastic as these two elements can be hazardous when they come in contact with the heat produced inside a microwave.
  3. Microwave the cardboard for relatively short durations i.e. 60 to 90 seconds for most of the cases. It can be nuked for 120 seconds for liquid drinks or beverages.
  4. Take out any paper, plastic or metal pieces before you microwave the cardboard. For example, remove the plastic lid of the disposable coffee cups, plastic pizza box holder or metal clip used to securely fasten the lid before microwaving it.

Microwaving Cardboard: Final Summary

It is clear from the above explanation that you need to make sure to read the label for manufacturer instructions before you microwave cardboard. Otherwise, it is better to transfer the food or beverages to a microwave-safe cup, bowl or plate to reheat. It is better for your own personal consumption as well as for the safety of the microwave oven.

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

If the cardboard is coated with waterproof lining such as wax or plastic, then it is not recommended to heat in the microwave. The coating can melt and contaminate food with chemical compounds.

Microwaving cardboard can be either safe and hazardous to your health. Review the type of cardboard and the potential hazards associated with using cardboard that has not been properly tested in the microwave. 

Richard Hotte

Friday 18th of November 2022

I have been poison cooking chicken wings in a take out box in a microwave, I was sick for 3 days , than I was ok but not completely well , than 3 months got really really sick , got sick for 4 months than got better , than got sick again one year and 1/2 later I am still sick and feel not good at all with pain in my belly , fatigue and lower back pain