Can You Put A Plastic Cup In The Microwave? (Easy Way To Tell)

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If you’re like most people, you probably have a few plastic cups lying around your kitchen. Maybe you are trying to reheat a coffee in a Starbucks plastic cup or melt some butter in a plastic measuring cup. And also like most people, you’ve probably wondered if it’s safe to put that plastic cup in the microwave.

Well, plastics are complicated so we took a deep dive into the science behind plastics to really give you an accurate answer. In this article, we’ll go over what is safe to put in the microwave and an easy way to tell if an unmarked dish is microwave safe. And as a general disclaimer, we always tell people to err on the side of caution when microwaving unmarked dishes.

Can You Put a Plastic Cup In The Microwave?

Most plastics should not go in the microwave. This is due to Bisphenol A (BPA) – a chemical compound that makes plastic hard and clear. BPA can leach into liquids or food that’s stored in plastic containers or cups and putting a plastic cup that contains BPA will exponentially increase the risk that BPA gets into your food.

Most companies have caught onto the harmful effects of BPA, so many plastic cups on the market today are BPA-free. While that is a move in the right direction, even though many plastic cups are BPA-free does’t mean they should go in the microwave.

That’s because there is more to worry about that just BPA. The new main concern is a chemical compound called phthalates or even the BPA alternatives that are used in BPA-free plastics that can release into foods when you microwave them.

To really know if a plastic cup is safe to put in the microwave, you need to know the type of plastic it is made of. As if this wasn’t complicated enough, there are 7 different types of plastic today. The only type of plastic used in food service that is generally microwave safe is plastic #5 (polypropylene).

Most microwave-safe plastic food containers that are actually made of #5 plastic are bento boxes or meal prep containers. Something like the option below is your best bet if you want something plastic that can go in the microwave.

Our Top Pick
Microwave Safe Plastic Food Storage Containers - BPA Free
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Can You Put a Red Plastic Cup In The Microwave? (Solo Cup)

Red Solo plastic cups should not be put in the microwave. Red Solo cups do not contain any BPA like some other plastics. Since microwaves are all different with different power levels, and red Solo cups are not made to withstand high heat.

Remember how we said there are 7 different types of plastic and only #5 is generally microwave safe? Well, red Solo cups are made of polystyrene (#6 plastic), a very common plastic that is used to make many consumer goods. So, therefore they are not microwave safe (take our word for it).

Here is another cool piece of plastic science for you: Polystyrene is also made into a foam material to create the annoying stuff call styrofoam that is in every delivery package you receive. Yup, packing peanuts are the distant cousin of your favorite party cup.

Can You Put a Plastic Starbucks Cup In The Microwave?

In fact, the clear plastic cups at Starbucks ARE microwave safe. Starbucks clear plastic to go cups are made of polypropylene (#5 plastic) which is the only plastic categorized as microwave safe.

Polypropylene does not absorb the energy produced by microwaves, and therefore is the only suitable type of plastic that is recommended for microwave use. However, the reusable Starbucks plastic cups are made of a different material that is NOT microwave safe.

If you want to reheat your coffee from Starbucks, it is always best to just pour it into a ceramic coffee mug before placing it in the microwave.

Can You Put a Plastic Measuring Cup In The Microwave?

Since there are so many different brands of measuring cups available, it really depends. Most models of plastic measuring cups available are not labeled specifically as microwave safe, so it is best to assume that the plastic measuring cup you have at home is NOT microwave safe.

We dug through some of the most popular options available on Amazon and only found 1 that was specifically labeled as microwave safe! The Norpro measuring cup shown below is made up of polypropylene #5 plastic (the safest bet).

Norpro 4-Cup Capacity Plastic Measuring Cup
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While some plastic measuring cups like the Norpro may be microwave safe, the majority are not. So, when it comes to measuring cups, you are much better off skipping the plastic and using a glass option like the one below.

Our Top Pick
Pyrex Glass Measuring Cup Set (Microwave Safe)
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How Do You Know If a Dish Is Microwave Safe?

How Do You Know If a Dish Is Microwave Safe?

The best way to tell if something is microwave safe is if it is clearly labeled as “Microwave Safe” on the dish. There is also a test you can do on a dish if it is not labeled to check if it is microwave safe. However, you must watch closely and stop the process at any moment if you see any smoke or sparks in the microwave.

The proposed test will help to identify whether a given dish is made of materials that absorb and retain heat, or if it instead allows heat to pass through. In order to carry out the test, you will need the dish in question and a cup or glass that is safe to use in a microwave.

  1. Place a microwave-safe cup or glass filled with tap water in the microwave oven.
  2. Place the dish in question next to the microwave-safe cup in the microwave.
  3. Turn on the microwave with both dishes inside for roughly one minute. Watch them closely to make sure no sparks occur.
  4. If the temperature is warm or hot, the microwave is not safe to use. If the temperature is cold and the cup of water is hot, then the dish is safe to use in the microwave.

Can You Put Aluminum Foil In The Microwave?

According to the USDA, aluminum foil can be used safely in small amounts in a microwave oven. Placing small pieces of foil over areas of food such as poultry drumsticks and wings can help prevent overcooking.

But aluminum foil can be easily overwhelmed by electrical currents in a microwave, causing them to heat up quickly and potentially start a fire. If the foil is crinkled so that it forms any sharp edges, the electrical current running through it can cause sparks.

If these sparks hit something else in the oven, such as wax paper, a fire may start. So, you must be very careful when using even small pieces of aluminum foil in the microwave. When it comes to microwaves, it is best to exercise caution and avoid placing any kind of metal inside.

For a deeper dive into what metals are microwave safe, check out – Can You Put A Metal Bowl In The Microwave? [Solved]!

Which Materials Can Go In The Microwave?

If you’re wondering whether that dish you just pulled out of the cabinet is microwave safe, don’t worry – most glass, ceramic and heatproof dishes are microwave safe. The same goes for oven cooking bags, wax paper, parchment paper and vented plastic bags.

Be careful though, not everything that can go in the dishwasher is safe for the microwave. These appliances are very different and allow different materials to be used inside.

Just be sure to check that any paper products you’re using are specifically approved for microwave cooking.

The Wrap Up

We did a deep dive into the science behind plastics to really give you an accurate answer in this article. To sum it up, some plastics might be safe for a microwave but most are not. And if you’re ever in doubt, it’s always better to err on the side of caution and just use a ceramic or glass bowl!

About Patrick Hardi

Patrick Hardy is a graduate of the Inspection Certification Associates online home inspection course. He has gone on to start H & H Home Inspections, a multi-inspector home inspection company based in Central Florida that performs home inspections, commercial property inspections, WDO, wind mitigation inspections, and 4-point inspections. In addition to performing classroom training for ICA, Patrick also teaches continuing education classes for home inspectors.