Can You Microwave Cardboard – Is It Safe?

Although you can always use a ceramic bowl or plate to microwave your food, it also means that you’ll have to do a bit of cleanup after. Sometimes, you just might not be in the mood to do the dishes. That’s why you might be searching for an alternative. One of the alternatives that might cross your mind is cardboard containers.

You can eat food out of a cardboard container and simply throw it in the trash once you’re done using it. That’s a very practical solution. But is it safe to do? Can you microwave cardboard containers?

Can You Microwave Cardboard – Quick Answer

Yes, you can generally use cardboard containers to reheat food in a microwave. However, you shouldn’t keep the container in your microwave for more than two minutes. Otherwise, there is a risk of the cardboard overheating and potentially even starting a fire.

Is It Safe To Microwave Cardboard

Yes, it is safe to microwave pure cardboard. As long as it is made from wood fibers and doesn’t contain any coating or ink, you’ll be able to safely reheat food in a cardboard container. You should avoid cooking food in a cardboard container at all costs. Only use these types of containers for reheating food.

How Does Cardboard Interact With Microwaves

A microwave oven is a wonderful appliance. Most people aren’t too familiar with how it actually works. Instead of evenly spreading heat like a traditional oven, these appliances use microwave energy to heat food. Microwave energy essentially represents electromagnetic waves that get absorbed by fat, sugar, and water molecules that then start to move rapidly and generate heat.

As the molecules generate heat, they will then spread to the cardboard container. The cardboard will gradually begin to lose its moisture content until it’s dry. You should remove the cardboard and the food from your microwave before that happens because once it is completely dry, it may start a fire.

Can Cardboard Catch Fire In A Microwave

It may seem dangerous to put cardboard in a microwave due to a potential fire breaking out. People are familiar with how flammable both cardboard and paper are, which is why it may seem counterintuitive to heat them at high temperatures in a microwave oven. Thankfully, these appliances work a bit differently and won’t cause a fire to break out when you’re microwaving cardboard as long as you don’t keep the container inside for too long.

According to a study published by the Swedish University of Agricultural Sciences cardboard has a moisture level of 10%, which means that it won’t catch on fire too easily if it’s in a microwave. However, you should keep the power level settings of your microwave low. You also need to ensure that the cardboard container doesn’t stay in the microwave for more than two minutes while checking to see whether it’s overheated every 30 seconds.

Cardboard Containers Used in Food Prep

Cardboard containers are quite popular for the temporary storage of food. Most people immediately associate cardboard containers with pizza boxes, but they are now more frequently used by restaurants of different cuisines. Cardboard is often used to make disposable cups, cereal boxes, and recyclable bowls.

The primary reason for the popularity of cardboard containers is cost-effectiveness. Although these containers are great if you order takeout, you might wonder what you should do when you want to reheat leftovers.

In this case, you may be tempted to reheat the leftovers while they’re still in the cardboard container. However, this is something you should do only if the cardboard is microwave safe. There are two main types of cardboard containers used in food prep – coated and uncoated.

Coated or Prefabricated Containers

Coated containers generally are not safe for use in a microwave. Even if you want to quickly reheat the food in such a container, you shouldn’t do it. The reason why you should avoid reheating food in a coated container is that it can contain hazardous plastics that will contaminate your food.

Uncoated Cardboard

Uncoated containers are made from pure cardboard. In other words, they contain only fibers from trees and plants. Uncoated cardboard is generally deemed safe for use in a microwave as long as it doesn’t contain any printed ink. Although they are safe for use in a microwave, you shouldn’t keep them inside the appliance for too long. In case you keep cardboard containers inside a microwave for more than a few minutes, you risk a fire breaking out in your kitchen.

Is Coated Cardboard Toxic When Heated

Yes, coated cardboard is toxic when heated. All it takes is the container to have a thin layer of plastic or wax for it to be harmful to your health. Once the temperature increases to a certain point, the layer of wax or plastic will begin to melt and combine with your food. This can lead to both small and serious health problems.

How To Tell If Cardboard is Microwave Safe

The best way to tell whether a cardboard container is microwave safe is to check whether it features a symbol with three or more squiggly lines. The squiggly lines represent what’s known as the microwave-safe symbol. In case a container is made only from wood fiber, it’s likely to have this symbol featured on it.

However, there are many cardboard containers that are made from recycled materials. These materials can include small amounts of metal, which you should never put inside a microwave. It’s recommended that you always avoid putting a cardboard container inside a microwave oven if it doesn’t have the appropriate symbol.

Sometimes, a container may look fine but won’t have the microwave-safe symbol featured on it. Although it may be tempting to use it for reheating food, it’s best to simply transfer the food to a microwaveable bowl. If you put the wrong type of cardboard in your microwave, you risk your food getting contaminated and making you sick.

When Not To Microwave Cardboard

There are some instances in which you shouldn’t microwave specific cardboard containers. Plain cardboard containers are generally safe to use. But in case the container features any type of adhesive, it can potentially release toxic chemicals in the microwave and contaminate your food.

You should also avoid microwaving any cardboard containers that have ink printed on them. Print ink can also be leeched and release toxins in the food at a certain temperature. Not only that, but the ink can also be flammable and may even start a fire.

Some cardboard containers feature plastic or wax linings, which can also be harmful. The moment the plastic or wax starts melting, it will contaminate the food you’re heating. You can tell whether a cardboard container is coated in plastic simply by touching it. In case it feels very smooth to the touch, it’s likely coated in plastic.

Finally, there are certain cardboard containers that feature metal handles. As you most likely know, metal is something that should never go in a microwave oven. If you place a container with metal handles in your appliance, you might see sparks of electricity flying as soon as you begin heating the food.

Tips: Microwaving Food In Cardboard Containers

I’ve compiled a list of helpful tips for microwaving food in cardboard containers. I find all of these quite practical and I’m sure they will help you have a more safe and overall better experience when it comes to microwaving food in cardboard.

1. The most important tip you need to remember is to check whether the cardboard container contains any labels. You won’t always find a label, microwave-safe symbol, or instructions on whether the container is safe to use in a microwave. However, if there is any information available, it will help you decide what to do.
2. Make sure to avoid microwaving any cardboard containers that contain wax or plastic coating. You can check whether they’re coated simply by touching them. If they feel very smooth to the touch, it means that the containers are coated.
3. Keep the power level set low when you heat food in cardboard containers. In case you set the power on medium or high, the moisture in the cardboard will get absorbed extremely quickly. Once that happens, it may transform into a fire.
4. Always monitor the food that you’re reheating in a cardboard container. Since you shouldn’t keep it inside the microwave for more than two minutes, it’s best to stay right next to the appliance during that time period. Make sure to check whether the cardboard is overheated every 30 seconds.
5. You should never microwave cardboard on its own. There should always be food in the container. If you were to microwave only cardboard, it would catch on fire very quickly.
6. Don’t microwave cardboard containers that are closed. You should always keep them open to avoid heat building up inside the container and potentially causing it to burst. When the container is closed, the pressure inside it will rise rapidly since there will be no way for it to get released. In this case, the container may either burst while it’s in the microwave or you could encounter a huge cloud of hot steam as soon as you open the container. Neither of the two outcomes is good.
7. One of the risks associated with heating foods in a cardboard container is that the grease and oil from them can get onto the container and cause it to heat more quickly. That’s why I always grab a piece of parchment paper and line a cardboard container with it before I place it in my microwave. This gives the container another layer of safety and prevents it from having direct contact with the food.

FAQs Is It Safe to Microwave Cardboard