Can You Microwave Cardboard?

It’s the end of the workday. You’re exhausted—and ready to flop down on the couch and stream the new Julia Child series on HBO Max. It’s the perfect night to pop leftover takeout into the microwave. But can you microwave cardboard?

The good news: you probably can. But it’s best to spend a few extra seconds checking what your container is made of to keep your food, and your microwave, in tip-top shape.

Learn how to microwave leftovers the right way.

Is It Safe to Microwave Cardboard?

If you’re using microwave-safe cardboard (meaning cardboard that is pure cellulose), then 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 cardboard. Keep your microwave on a low power setting, too.

But if you need to heat something up for longer, it’s a better bet to transfer the food to another microwave-safe container. Why? Because cardboard is flammable, especially at temperatures of over 400°F or for prolonged periods of time—this causes the moisture level in the cardboard to drop, making it more likely to catch on fire.

Can a pizza box go in the microwave?

Pizza boxes are generally safe to pop in the microwave, as long as you can find a microwave-safe label or written instructions. While many brands make boxes that can be reheated safely, others might include plastic or metal. (Learn whether you can put aluminum foil in the microwave.)

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 should not microwave:

• Cardboard that has glue or another adhesive. This can release chemicals into your food.
• Cardboard that has ink printed on it—it can also also release chemicals into your food.
• Cardboard that has a lining. Wax and plastic linings can release chemicals and fumes into your food (here’s more about whether you can microwave plastic).
• Takeout containers with metal handles: Hi, 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 to know about glass in the microwave.

Tips for Microwaving Cardboard

• Look for a microwave-safe label on the cardboard. If it’s not there, move your food or drink to another microwave-safe dish before heating.
• Make sure there’s food in your cardboard container (that’s the point, after all!) The food helps absorb the microwaves to reduce the risk of the cardboard catching fire.
• Line your container with a paper towel or napkin. This will help soak up oils, which, when they soak into the cardboard, increase the speed at which the cardboard heats and increases the risk of fire.
• Make sure to monitor your food—when heating up cardboard in a microwave, don’t leave it unattended.