' ); } ?>

Can You Put Cardboard In The Microwave? Ultimate Guide

This post may contain affiliate links. Please read my disclosure policy.

Microwaves are a staple in most kitchens these days. They provide a quick and convenient way to heat up leftover food or cook a hot meal in minutes.

However, there are some limitations on what can and cannot be microwaved safely.

One common question is whether cardboard can go in the microwave. Let’s take a closer look at whether putting cardboard in the microwave is a good idea.

The Composition of Cardboard

Cardboard is made from layers of paper pulp that are pressed and glued together.

The typical materials used to create cardboard include:

  • Cellulose fibers from wood, cotton, hemp, or other plants
  • Binders like lignin hold the fibers together.
  • Fillers like kaolin clay or calcium carbonate
  • Sizings like starch or PVA to control absorbency
  • Dyes or pigments for color

So cardboard contains materials that are designed to be stable, absorbent, and hold their shape when dry. But how do these materials react when subjected to microwave radiation?

Is a cardboard microwave safe?

In general, it is not recommended to put cardboard in the microwave.

Here are a few reasons why:

Fire Risk

One of the biggest risks is that cardboard can catch fire in the microwave. Cardboard contains cellulose fibers and binders that are meant to hold their structure when dry.

However, when subjected to microwave radiation, the water molecules in the cardboard absorb the energy. This makes the cardboard heat up very quickly, potentially even causing it to burn or scorch.

Microwaves are designed to heat foods that contain adequate moisture. But cardboard has a very low moisture content. This uneven heating can create hot spots that ignite the cardboard. A small flame could then spread or cause other items in the microwave to catch fire as well.

Chemical Leaching

Another concern is that chemicals from dyes, binders, or other materials in the cardboard could potentially leach out when heated in the microwave. If these leaked onto food, it could be harmful for consumption.

Specifically, recycling symbols and ink on cardboard often contain heavy metals like lead, mercury, and cadmium. Subjecting cardboard with these to microwave radiation can make the chemicals more likely to migrate.


Cardboard in the microwave is also likely to create a big mess. The cardboard will absorb moisture from the food, causing it to warp, collapse, and degrade.

This could make the cardboard soggy and fall apart. Bits and pieces of cardboard debris would end up dispersed throughout your food.

Sanitation Issues

From a food safety standpoint, microwave experts caution against using any porous material for cooking.

The small pores in cardboard can harbor bacteria. Putting cardboard in direct contact with food during microwaving could lead to contamination.

Alternatives to Putting Cardboard in the Microwave

Instead of putting cardboard directly into the microwave, consider some safer options:

  • Use paper plates or bowls designed to be microwave-safe. Avoid recycled paper products.
  • Place a paper towel between food and cardboard to create a protective barrier.
  • Transfer food onto a ceramic, glass, or microwave-safe plastic dish before heating.
  • Cover food with a paper towel or wax paper if reheating on cardboard.
  • Use the cardboard to retain shape or structure when cooking something else in the microwave.

With a little creativity, you can still take advantage of cardboard’s stability and structure. Just be sure to take precautions against direct microwave exposure. Monitor the entire cooking time and never microwave cardboard alone.

Tips for Microwaving Food Safely

Microwaves can be a safe and convenient cooking method when used properly.

Follow these tips for the best results:

  • Only use cookware and materials specifically labeled for microwave use. Look for the microwave-safe symbol.
  • Avoid metal cookware and accessories, which can lead to arcing and fires.
  • Use the minimum amount of microwave time needed to heat the food. Extended cooking can dry out certain foods and make them prone to catching fire.
  • Allow standing time before eating so the temperature can be evenly distributed. Microwaved foods can have deceptive hot and cold spots.
  • Cover foods while cooking to retain moisture and prevent splattering. Use vented lids or microwave-safe plastic wrap with a corner folded back.
  • Stir and rotate foods midway through cooking for even heating.
  • Check the internal temperature of meats and other foods before eating to ensure they are fully cooked.
  • Clean the microwave regularly to remove any dried food splatters that could catch fire.

Following basic precautions allows you to harness the speed and simplicity of microwave cooking safely.

Frequently Asked Questions About Cardboard in Microwaves

Here are some common questions about the safety and risks of microwaving cardboard:

Can you put an empty cardboard food box in the microwave?

No, it is not safe to put any type of cardboard into the microwave, even if no food remains inside. Empty cardboard containers can still ignite, off-gas chemicals, or make a mess in the microwave.

What if the cardboard has a plastic coating or liner on it?

A plastic coating or liner may help prevent the cardboard from directly absorbing moisture and heating unevenly.

But it would still be risky, as the cardboard inside could heat up, ignite, or release chemicals. Play it safe, and don’t microwave cardboard of any kind.

Is it okay to microwave cardboard for a short time, like 10 seconds?

It’s still inadvisable to microwave any cardboard, even for a short burst. The uneven heating and fire risks remain.

Ten seconds can be long enough for cardboard to scorch.

Can I cover food with cardboard while microwaving?

Directly covering food with cardboard is not recommended, as the cardboard could ignite, leach chemicals, or get soggy from steam.

Instead, use paper towels, wax paper, or a ceramic plate to cover foods when microwaving.

What if I wave a piece of cardboard through the air inside a running microwave?

Never put any object inside a running microwave, even for a few seconds. This is extremely dangerous, as it could disrupt the microwave and radiation patterns.

At minimum, it would create non-uniform hotspots that could damage the appliance or anything inside it.

The Bottom Line

Microwaves are designed for heating foods, not cardboard. While cardboard won’t immediately burst into flames, the risks make it unsuitable for microwave use.

Instead, rely on materials designed to be microwave-safe and take steps to prevent cardboard from being exposed to microwaves.

With proper precautions, you can safely harness the speed and convenience of microwave cooking.


How useful was this post?

Click on a star to rate it!

Average rating 0 / 5. Vote count: 0

No votes so far! Be the first to rate this post.