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Can You Microwave Styrofoam Cups?

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Have you ever used a styrofoam cups in the microwave? Let’s discuss the best way to reheat coffee in the microwave if you have leftover coffee inside a styrofoam cup.

Styrofoam cups are made of polystyrene, which is a type of chemical compound that is not microwave safe.

Styrofoam is a the of closed-cell extruded polystyrene foam that is labeled under a trademarked brand. There are many different polystyrene foam cup manufacturers, however only The Dow Chemical Company manufactures Styrofoam.

Styrofoam cups are sturdy and heat resilient, and the cups generally feel cool when microwaved. However, it is important to discontinue microwaving when the cup begins to pit or show signs of damage. 

What is styrofoam cup made out of?

The styrofoam cups are widely used for to serve coffee and hot chocolate. They have also been used as affordable disposable bowls to serve soups, stews, and chili.

Styrofoam consists of 98% air, which makes it extremely lightweight. Because air is considered a good tool for insulation. styrofoam cups boasts reliable insulation properties that help to keep beverages hot or cold for longer periods of time.

Styrofoam is made out of harmful petroleum-based product that is made from chemicals like styrene and benzene. Although styrofoam is lightweight and durable, it is bad for the environment because it is not recyclable. 

Styrofoam is cheap, strong and keeps coffee hot for extended amounts of time. But does that mean it’s safe to microwave styrofoam cups filled with coffee?

Is it safe to microwave styrofoam cups?

Not all styrofoam reacts the same way in the microwave. Before you proceed, you may want to double check for the microwave safe symbol on the bottom of the cup.

If the styrofoam cup doesn’t have a microwave safe label, then it’s best to assume that the cup is not recommended for use in the microwave; not even for 20 seconds!

Styrofoam is a type of petroleum based plastic. Under conditions of extreme heat, chemicals can leach out of the products and enter into the liquid that it holds. 

Can you microwave styrofoam coffee cups?

It is safe to assume that most styrofoam coffee cups are not microwave-safe. You can evaluate individual coffee cups based on the recycling number system and type of plastic stated on the bottom of the container. 

In general, styrofoam coffee cups are polystyrene or plastic recycling number 6, which is not safe to use in the microwave. It is recommended to avoid heating in the microwave because it contains potentially carcinogenic chemicals that may leach into food and beverages. 

Always check the recycling number on the bottom of the container to evaluate if the plastic compound is considered safe to use in the microwave. 

The number corresponds to the type of chemical compound:

  • 5 is polypropylene, PP, which is considered microwave safe.
  • 1, 2, 4 are sometimes microwave safe. 
  • 3, 6, 7 are not microwave safe.

Things to know before microwaving styrofoam cups

Because styrofoam cups last longer than any other material and are great to insulate hot coffee, that doesn’t necessarily mean that it can be microwaved with food and beverages inside.

Here are essentials things to know before microwaving styrofoam cups:

  • Transfer food and drinks from styrofoam cups to containers like glass cups, pyrex or ceramic mugs.
  • Check to see if there are scratches or cracks in the surface of the foam cups. Old, damaged or degraded styrofoam cups might potentially leak harmful chemicals into the hot coffee.
  • Never reheat styrofoam cups more than once in the microwave.
  • Reduce the microwave power level to medium if you must use a styrofoam cup for reheating food and beverages.
  • Use 30 second increments when microwaving styrofoam cups.
  • Reheating can create uneven heat pockets in food items, so give it a stir after each interval to avoid superheating
  • Use caution when removing the container from the microwave, the outside of the foam cup may be cool to the touch but the food item can be extremely hot!

Avoid microwaving polystyrene coffee cups when possible. Most styrofoam cups do not have microwave-safe labels, which makes them potentially hazardous for reheating food and drinks. 

If the styrofoam cup has a microwave-safe label, that guarantees it has been tested and shouldn’t pose any styrene-related health risk. 

On the condition that you been microwaving styrofoam cups without any problems, then continue to proceed cautiously. However, if you have any concerns about the risks of overheating foam cups in the microwave, then its best to transfer the drink into microwave-safe cups prior to reheating.

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