Can You Microwave Cardboard Cups?

We’ve all been there. You grab a nice hot cup of coffee from your local cafe, get sidetracked on the way to the office, and then realise it’s tepid by the time you get there. Urgh.

Fortunately, your office has a microwave, but can you actually microwave the cardboard cup you’re holding? No one wants to be the one who trashed the office microwave after all!

In this article, I’ll explain everything you need to know to help you zap that coffee with confidence.

An exterior shot of a Starbucks coffee shop

About Cardboard Cups & Microwaves

For the most part, a cardboard cup is perfectly fine to put in the microwave. Generally speaking, cardboard is fine to nuke as it doesn’t contain anything that reacts badly with the appliance.

There are a few “buts” here, however.

Certain factors may affect the safety of microwaving a cardboard cup, which I’ll cover off in the next section.

When It’s Not OK To Microwave Cardboard

There are certain things you need to look out for before heating up your drink in the microwave:

  • Decorative elements: Are there any metallic or foil decorations on the cardboard cup? If so, don’t microwave it. These can create unsettling sparks, or even damage the microwave.
  • Wax / plastic coatings: Some cardboard cups from popular chains have a wax or plastic coating. This helps prevent leaks, but isn’t so good for your microwave. 
  • Damaged cups: If the cardboard cup is damaged in any way, don’t put it in the microwave. The extra heat may cause it to fall apart completely, making a massive mess in the process. Plus there’s the risk of you getting scalded by the hot drink.

How to Microwave Cardboard Cups Safely

To avoid any possible problems, keep these tips in mind:

Check the label: If you see a microwave or wavy line logo on the cardboard cup, that’s a sure-fire sign that it’s fine to be reheated this way. If in doubt, you might consider transferring the drink to a vessel that you know for sure is microwave-safe.

Reheat in bursts: Microwave your drink for just 30 seconds and see if it’s drinkable. If not, only increase the time by 15-30 second intervals to avoid overheating the contents and the container.

Keep an eye out: One of the appeals of a microwave is that you can fire-and-forget common tasks. Don’t do that in this case. Instead, keep an eye on what’s happening so you can hit the stop button if something’s going badly wrong.

You might also consider some alternatives to reheating your cardboard cup in the microwave.

  • Get a microwave-safe mug: These are readily – and inexpensively – available. Pour your drink into one of these, and then zap it in the microwave.
  • Use a beverage warmer: Equally popular are beverage warmers. Keep this on you and you can simply place it around the cardboard cup to keep your drinker hotter, for longer.

If you’re hesitant to microwave a cardboard cup at all, consider one of these two alternatives instead.

Wrapping Up

So, can you microwave cardboard cups? For the most part, yes you can but as you know now there are a few very important caveats.

Check there’s no metallic or foil decoration on the cup, watch out for waxy coatings, and don’t leave it unattended if you do decide to microwave it.

Ideally, you’ll simply transfer it to a container you know is safe to go in the microwave, or grab a mug warmer. Both are very safe options, and that way you’ll never even need to ask this question!