Can cardboard go in the microwave?

You need an easy dinner and have leftover takeout in the fridge. But can you heat cardboard in the microwave? Here’s how to reheat food safely. Can cardboard go in the microwave?

It’s the end of the workday. You’re exhausted and ready to kick back on the couch and stream Julia Child’s new series on HBO Max. It’s the perfect night to microwave takeout leftovers. But can you heat cardboard in the microwave?

The good news: probably can. But it is better to spend a few more seconds to check what the container is made of to keep the food and the microwave in perfect condition.

Learn how to cook leftovers in the microwave the right way.

Is it safe to heat cardboard in the microwave?

If you are using microwaveable cardboard (i.e. cardboard that is pure cellulose), you can microwave it for short periods of time. Just keep it between 60 and 120 seconds, and check every 30 seconds to reduce the risk of overheating the carton. Keep your microwave on a low power setting as well.

Can cardboard go in the microwave

But if you need to heat something for a longer time, it is better to transfer the food to another microwave-safe container. Why? Because cardboard is flammable, especially at temperatures above 400°F or for extended periods of time, this causes the moisture level in the cardboard to drop, increasing the likelihood of a fire.

Can a pizza box go in the microwave?

Pizza boxes are generally safe to microwave, as long as you can find a microwave-safe label or written instructions. While many brands make boxes that can be safely reheated, others may include plastic or metal. 

Make sure the box is in the microwave for less than a minute. (And let’s be honest, there are plenty of other delicious ways to reheat pizza)

Types of Cardboard You Can’t Microwave

Here are the common cardboard containers you not microwave:

  • Cardboard that has glue or other adhesive on it. This can release chemicals into your food.
  • Cardboards that have ink printed on it can also release chemicals into food.
  • Cardboard that has a liner. Wax and plastic coatings can release chemicals and vapors into food (here’s more on whether you can microwave plastic).
  • Takeout Containers with Metal Handles: Hello, Chinese takeout. Metal is a no-go in the microwave.

By the way, here’s the scoop on whether you can microwave paper plates and what you should know about microwaving glass.

Tips for Microwaving Carton

  • Look for a microwave-safe label on the carton. If it’s not there, move your food or drink to another microwave -safe dish before heating.
  • Make sure there is food in your cardboard container (that’s the point, after all!) Food helps absorb microwaves to reduce the risk of the cardboard catching fire.
  • Cover your container with a paper towel or napkin. This will help absorb oils which, when they penetrate the cardboard, increase the rate at which the cardboard heats up and increases the risk of fire.
  • Be sure to keep an eye on your food: When heating cardboard in a microwave, don’t leave it unattended.

Things to Know About Microwaving Cardboard

Not all cardboard boxes can be heated in the microwave. If the container is microwave-safe, here are several things to keep in mind when microwaving cardboard.

Can cardboard go in the microwave

  • Check the label– If it’s a cardboard pizza box, there’s a chance you’ll find the label with instructions about whether it’s dangerous to microwave. Always check for a small three-wave icon indicating microwave safety. The icon is a microwave symbol, and if it is not available, consider looking for written instructions.
    The instructions section will give you details on how to heat your food in the oven, stovetop, and microwave in each food-safe carton.
  • Check for metal: Some cartons come with traces of metal, which are definitely not microwave safe. Check to confirm that noxious traces like aluminum foil are not present on the packaging.
  • Chemicals: Soup Containers, Cups, and Bowls Should Be AvoidedThis notion should apply to ink-printed cardboard boxes and foam of any kind. Added ingredients can release dangerous vapors or melt, which could mix potentially harmful chemicals with food.
  • Microwave temperature– Check your appliance settings and set the level of loss possible when heating a meal in a cardboard box. In general, set the temperature to low power on your microwave when using cardboard to reheat food.
  • Type of food: Avoid heating foods with a high water content because heat is generated and radiated relatively slower if the box is closed. A closed box means that a lot of pressure will try to escape, causing an explosion. Also, the hot liquid could compromise the integrity of the cardboard material and cause it to soak through and break.

Microwaving Cardboard Food: Final Thoughts

It can be tricky to determine if it’s safe to microwave leftover cardboard food. From pizza to pasta, carton packs are eco-friendly and also keep fresh food hot for short periods of time.

However, whether or not it is safe can be a vague gray line. Cardboard boxes do not contain a large number of water molecules, so it may take longer to heat the food.

If you are concerned about food getting soggy due to fewer water elements, the cardboard absorbs the steam to prevent it from igniting so that your food doesn’t get soggy. 

When using microwaveable cartons, moderation at a lower temperature and a short time helps to avoid potential fire hazards. 

Can cardboard go in the microwave

Always check to see if the box consists of metal or hazardous components such as aluminum foil or plastic and wax coating. These hazards will determine whether or not it is safe to microwave the carton of food.

Finally, do not close the lid of the box if the food has a high water content. Closing the lid while reheating can trap steam pressure, which can cause an explosion. 

From the explanation derived above, the right thing to do before microwaving cardboard boxes is to consider reading the instructions and looking for the microwave safe symbol. Making sure the cup, carton, bowl, or plate is microwave-safe will help prevent a potential microwave hazard and maintain your good health. 

If you are using a cardboard box made from pure cellulose or fiber material, you should rest easy knowing there is little risk involved. Make it a habit to check the carton before microwaving your food. 

The outside of the box will be labeled with instructions that clarify the problem to help you avoid potential mishaps. If you’re not sure, simply reheat leftovers in a microwave-safe bowl for risk-free enjoyment.




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