Can You Microwave Cardboard?

If you have eaten out, you likely have brought leftovers home with you at some point. When you want to reheat these leftovers you might have considered using the container they are in instead of getting a plate or bowl dirty. But can you put cardboard in your microwave?

Cardboard is generally safe to microwave. Make sure that there is food or drink in the cardboard and that the cardboard is not left in the microwave for several minutes at a time. Avoid microwaving items like plastic, metal, or styrofoam with cardboard.

While you might be worried, as long as you keep an eye on the cardboard while it is in your microwave, you are unlikely to experience any issues. A general rule of thumb is to check the cardboard container and see whether it is labeled microwave safe or not. Here are some more things to keep in mind about cardboard and your microwave.

Is Cardboard Safe to Put in the Microwave?

Whether you have leftovers or a freezer meal, there is a good chance that you will microwave cardboard. Specifically for restaurants, especially fast food restaurants, cardboard has become a popular storage container. However, sometimes you want to avoid creating more dishes, so you simply microwave your restaurant leftovers in the cardboard container they came in.

Luckily for you, cardboard is generally safe to put in a microwave. When microwaving cardboard, there are a couple of rules that you should follow. Cardboard should not be put in the microwave by itself, but instead should only be put in when it is holding food or drinks.

When microwaving cardboard, you should keep the microwave temperature low and should only microwave the food for 1 to 2 minutes at a time. If you would like to microwave the container longer than this, leave the container of food in the microwave for a minute or two to cool down before continuing to heat up the food.

Most types of cardboard are made from recycled cardboard or plant fibers. Both of these ingredients are safe to place in your microwave and do not release chemicals when heated. This means that you can store food in them, and heat that food up and there won’t be any contamination to the food. This makes cardboard a great option for reheating and is easier on the environment than plastic.

When Should You Not Microwave Cardboard?

While cardboard is a good container option for reheating food, here are some things that you should keep an eye out for that would make the cardboard inappropriate to use in a microwave.

The first thing that you should look out for are things that should not be placed in a microwave. If something is not safe in the microwave by itself, it still is not safe if it is included with cardboard.

The most common offender is metal. Metal is not safe to put in microwaves and can cause serious damage to them. Metal may be put in cardboard containers to provide structure and support. If your container has any metal in it, it is not safe to be used in the microwave. One place you might have seen this is in Chinese takeout containers. These containers often have metal handles that help to hold the takeout box together. In this case like these, you will have to transfer the leftovers to a different, microwave-safe container before placing them in the microwave. If you can tell that the only metal on the box is the handle, simply remove the container’s handle to make it safe to use in the microwave.

Other offenders are plastics and waxes. These show up in certain types of cardboard to make them more durable, or may just be a lining within the cardboard. If your cardboard has any sort of plastic with it, it should not be put in the microwave. Waxes and plastics melt at low temperatures compared to cardboard.

When plastics melt, they leak gasses that are toxic into the surrounding air. This means that any food within the container will be contaminated and you may breathe in toxic fumes while waiting for your food. An easy way to spot cardboard that has plastics is to look for shiny or smooth cardboard. These types of cardboard are not safe for use in your microwave, even for a couple of seconds.

The final thing to keep in mind is that you should not put cardboard that is labeled with “do not microwave” in the microwave. It might be a simple thing, but most cardboard manufacturers will label any of their cardboard products on whether they are microwave safe or not. A quick look at your cardboard container could save you a lot of future trouble as long as you heed the label.

Why Should You Be Careful While Microwaving Cardboard?

No product is safe 100% of the time in a microwave, no matter what it is. When you place something in the microwave, you are not just heading it up as you would in an oven or over the stove. A microwave will use high-energy microwaves that bombard whatever is put into the microwave.

These waves pass through the air and into any objects in their path. Liquids and solids trap these waves that rattle around between molecules. As molecules are hit more often and vibrate faster, they begin to heat up. These waves interact with sugars and oils within the food or drink, but most commonly are captured by water molecules. The water is heated and evaporates which warms the surrounding food. This is why if you leave food in the microwave too long it turns out dry, as all of the water has evaporated.

Your cardboard container will not be made with any sugar or oil but will have water molecules since it is made out of plant fibers. As the cardboard is left in the microwave these small drops of water will heat up and dissipate drying the cardboard out. Dry cardboard will begin to burn around 400 degrees Fahrenheit, posing a risk to your appliance and the home or apartment around it.

For these reasons, you should be careful when microwaving cardboard. Never microwave cardboard by itself, but always have food or drink in the cardboard. The food will catch microwaves, keeping the cardboard from drying out too quickly. Remember to not microwave cardboard for more than 2 minutes at a time. This will allow the cardboard to cool slightly and prevent it from reaching temperatures where it could catch fire.

What to Do If The Cardboard Catches Fire

Despite all of your best efforts, you may encounter an issue when using cardboard in the microwave. The most common issue is the cardboard catching on fire. If you encounter this, do not worry. It is quite easy to contain the fire as long as you are prepared.

The first thing to do to prevent this from happening is to stay near the microwave while you have food or cardboard inside. This can not only prevent fires, but you may also smell burning food and catch it before your meal is ruined. If you smell smoke or can see a fire starting, there are a couple of quick steps to follow.

  1. Turn the microwave off
  2. Unplug the microwave (if you can access the plug)
  3. Keep the door shut
  4. Wait until the fire is completely extinguished to open the door

By following these simple steps, you can contain the fire easily. Turning the microwave off turns the internal fan off, which limits the spread of the fire. Keeping the door shut smothers the fire and prevents it from spreading out into your kitchen. Remember to not open the door until you are sure the microwave is completely off. Open the door too early and you may reignite the fire.

But how big of a risk is it that your microwave will catch fire? In a study done by the National Fire Prevention Agency, they found that at least 90% of US households have a microwave in their home. However, only 4% of all cooking-related house fires were linked to microwaves.

What this means for you is that you have an extremely low chance of cardboard catching fire in your microwave. As long as you stay near the microwave and are aware of what is happening inside, there is little chance that you will have any issues while microwaving cardboard.

What Are Different Types Of Cardboard Food Containers

When looking around your kitchen, you will see a variety of different types of cardboard. While all of the different types of cardboard are similar, there are some types of cardboard that are better to use in a microwave than others. Some are safe to use but have issues that stop them from being the best, while others are not safe at all to use.

To identify the type of cardboard in your home, look for the thickness and color of the cardboard.

With that in mind, here are some of the different types of cardboard food containers that you might find around your home, and whether or not they are good to use in your microwave.

Paperboard Boxes

The first type of cardboard food container that you might encounter is paperboard boxes. These boxes are the ones that you will see at your local grocery store holding a beer or soda cans. These boxes are popular because they are cheap to make and are more durable than other forms of cardboard. Paperboard boxes will show up with other foods, especially seasonal or promotional items.

Paperboard is made by pressing sheets of cardboard together to create a thin and tough piece of cardboard. The paperboard will be about as thick as several sheets of paper put together. Paperboard usually comes in bright, shiny colors that are meant to catch shoppers’ eyes in a store.

You should not put paperboard in a microwave. The inks, waxes, and plastics that are mixed with the paperboard to make it visible, durable, and flexible are not supposed to be heated. Any one of these things should not be put in a microwave, and paperboard will generally have several of them.

Corrugated Cardboard Boxes

These are the traditional cardboard boxes that you will use to move or have lying around your home after your latest online purchase arrives. They are made by making a frame of cardboard pieces between two different sheets of cardboard. These cardboard boxes aren’t quite as strong as paperboard but are often used due to their low cost and ease of disposal.

However, you likely won’t want to put this type of cardboard in the microwave unless it was used to store food from a restaurant, as corrugated boxes are often used to store and carry pizzas. Even then, most pizza boxes (and other corrugated cardboard items) are too big to put in the microwave, so it is typically much easier to simply put your pizza on a plate or other material while heating it in the microwave.

You can put a corrugated cardboard box in the microwave safely. Before using it, make sure there aren’t any stickers, plastics, or metal that could make the box unsafe to use in a microwave.

Cardboard Cartons

Cardboard cartons are another type of cardboard container. These cartons combine cardboard with plastics and other materials to create flexible and durable containers. These cartons are often used to hold liquids like milk or juice.

These cartons are not safe to be heated in the microwave. The mix of different materials means that it cannot be treated like basic cardboard. The plastics and inks will melt before the cardboard will and can release toxic gases into your home. You should never put a cardboard carton in your microwave.

Cardboard Paper Plates

The final type of cardboard is paper plates made from recycled cardboard. Since the plates are primarily made up of cardboard, they are generally safe to be used in a microwave. The potential issue here is sometimes during the recycling process plastics and metals will get mixed in with the cardboard.

Most paper plate manufacturers are aware of this and will include information on the package on whether the plates are microwave friendly or not. Any paper plate that says it can be microwaved can be put in the microwave safely.