Can You Microwave Cardboard?

Cardboard has been used as a food container for many things, particularly greasy food like pizza or even spaghetti. Cardboard might be something you can easily tear, but this cheap container material can take the hot grease of many a food item or dish out there when you’re ordering something to go or for takeout. With that in mind, can you microwave a food item contained within a cardboard container? More importantly, should you?

Is cardboard microwaveable (or “microwavable”, either version is correct)? This article is here to find the truth about it. As a head’s up, you should know that only certain types of cardboard are microwavable, which means there are also types that aren’t.

Further reading: The Ultimate Guide to Choosing a Microwave Oven that Best Fits Your Needs

Can You Microwave Cardboard?

From my own initial personal experience, you can but it is best that you don’t and err on the side of caution. Use something that can take multiple reheatings like a ceramic or glassware plate. Even then, glassware should have a microwave-safe label itself for good measure.

Keep on reading to find out the difference between microwaveable and non-microwavable cardboard.

Microwave-Safe Cardboard: Most people nowadays in the 21^st Century like to get more things done in as little time as possible with as little effect as possible. If they can reheat something straight out of the box they would. But sometimes you can’t. Like with plastic and Styrofoam, certain cardboard can take a reheat or two with a microwave while other cardboard types are easily compromised by the hot food releasing hot grease on it, turning it into mulch.

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Directly Popping the Cardboard into the Microwave: How effective the cardboard is against the rigors of high-temperature-inducing microwave rays depends on the thickness and quality of the cardboard. The hot grease can seep into the board and turn it into mulch when everything is said and done. Then again, certain boxes that can fit into your microwave oven can maybe help heat up the food inside of them, like in the case of certain smaller-sized pizza.

What You Need to Know: You can microwave certain cardboard. The ones labeled “microwave-safe” in particular. It’s the same with plastic and Styrofoam, except it’s more about the microwave heat destroying the cardboard or making the grease hot enough to compromise its integrity rather than worrying about leaching plasticizers and dangerous chemicals into your leftover food. Otherwise, don’t put cardboard containers into the microwave oven.

Cardboard Boxes are Microwaveable or Not? Occasionally, you might wish to microwave containers made out of cardboard. Putting most cardboard containers into the microwave with greasy food is a bad idea. If they’re marked “microwave-safe” then you could use them. Even then, you shouldn’t microwave the cardboard for too long. You don’t want to risk hot grease destroying it and there’s also a chance of it catching fire, like when you use a magnifying glass to focus sunlight on paper.

Lower Settings Required: When microwaving microwaveable cardboard, you should also lower the settings and microwave the food for only a short period of time. The cardboard isn’t exactly as resilient as ceramic or glass against heat. It’s not even as durable as Styrofoam or plastic, especially hard plastic. It’s only good for takeout and containing hot food for a short time. The lower settings are a must. It’s cardboard. It’s supposed to be cheap and has limits in durability.

What Setting Precisely and How Short of a Time? According to the research we’ve conducted, how low the setting can be, and how short the time period is for microwaving depends on your microwave oven this time around. There are no concrete guidelines so a bit of experimentation or trial and error on your part might be called for. Microwave ovens vary in terms of power settings. In turn, most cardboard containers don’t tell you whether or not they’re microwavable or not, as though they’re not meant for microwaving in the first place.

If You Insist on Microwaving the Cardboard

It’s almost like microwaving cardboard is a no-no even though some cardboard is microwavable. With that said, if you insist on microwaving cardboard containers, you need to keep in mind the following things.

When to Put Your Box in the Oven: Always be aware that there are instances when it’s absolute nonsense to put your cardboard container into your microwave oven. It’s almost like putting the box in an open flame. You need to observe certain precautions before doing so. Microwaving leftover or cold food on a cardboard box provides an easy and cheap alternative to paper plates when reheating your dish, but you need to test your cardboard’s microwavable integrity first.

Remove All Metal Anything: Having metal anything inside your microwave oven is a no-no. That can cause sparks and all sorts of accidents that could destroy your leftover food, burn your cardboard box, and so forth. Make sure that the container has no metal on or within the box. It could have metal handles that can spark then explode within your microwave. It’s dangerous to microwave metal or even silverware in light of the potential damage it could do to the machine itself.

How Do You Know If Your Cardboard Contains Metal? Most metal parts on a cardboard takeout box are that of handles and the like you can easily remove. Then again, they could also be made of plastic that you should also remove for toxicity reasons. Inspect the box carefully to see any metal or plastic materials on it, even if it’s a simple staple wire or scotch tape. When it doubt, don’t microwave your cardboard container. You never know—it might contain small metal fragments due to the recycling or manufacturing process.

Wax or Plastic Coatings: Like with certain paper plates, there are cardboard containers that have wax, plastic, or foil coatings that could emit toxic fumes or melt as the heat goes up. An ordinary cardboard container with no coating is more microwavable compared to coated cardboard. The reflective coating cardboard containers—that you can put your spaghetti, ravioli, or lasagna in to prevent the grease from eating into the cardboard—is definitely not microwave-safe so don’t microwave that.

How Can You Tell If Your Cardboard Has a Plastic Or Wax Coating? There are containers that have a plastic coating with a reflective sheen on it like a foil to keep the liquid from your food like grease or sauces from seeping into the cardboard and turning it into mulch. Milk containers typically have such coated containers. Wax-coated or plastic-coated cardboard is slick and smooth to keep all that sauce and grease at bay. If you’re unsure of the wax coating on your cardboard, try scratching the cardboard surface with your fingernail. If something comes off then it’s coated.

Keep the Food Itself from Catching Fire: Don’t only safeguard the cardboard from catching fire. It’s also a possibility for the food itself to catch fire and then make the cardboard go up in flame itself. Due to microwaving cardboard being a safety hazard in and of itself, don’t commit double jeopardy and end up burning your food in the process along with the cardboard. The ceramic or glassware container has no such issues. Even if you ruin your food by burning it, the chinaware plate should the flames from getting any bigger.

How Long Can You Microwave Cardboard? It’s best to transfer food from a cardboard container to glassware or ceramic bowls/plates. Why? It’s such a bother to test cardboard to see if it’s microwaveable or not because reheating food on such a container for too long can damage the cardboard material anyway. It’s not like microwaveable plastic or Styrofoam that you can microwave for typical reheating times. Your food can also become inedible once the cardboard container burns or turns into mulch right on top of it.

How Long is Too Long for Reheating? 1-3 minutes maybe. Depends on the cardboard but if the cardboard is so thin it probably can’t take even the default minute-long microwaving process, you shouldn’t microwave it in the first place. Since microwaves vary in power, a minute from one powerful microwave oven might be too much for cardboard when compared to another weaker oven. At any rate, reheating food in the cardboard doesn’t save you much time at all. The effort of putting them in another container is worth it.

Final Thoughts

Even though certain cardboard containers for food takeout are non-microwavable, plenty of them are. Just check the packaging to see which cardboard type you ended up with. If it’s labeled as microwave-safe, feel free to reheat your food with it.

However, like with plastic, if it’s damaged or the grease has seeped into it then you shouldn’t use it and transfer the food to a plate or glassware for guaranteed safe reheating. The cardboard doesn’t leach the food with migrating chemicals or something but the hotter and greasier it gets the likelier it is to tear apart like a wet newspaper when you take it out of the microwave oven. Don’t reheat your food repeatedly with a cardboard container either. Once or twice is enough.

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