7 things that are definitely not safe to put in the microwave

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On one end, microwaves are a gift. They cook and reheat food quickly, and they can turn a sad meal into a happy one. At the same time, microwaves can completely ruin a meal if you don't understand what materials are safe and unsafe to zap. 

"Undeniably, microwaves are one of the most useful and popular kitchen appliances in history," says Mary Jones, editor at CookyMom.com. "While these appliances have proven so beneficial, there is a tendency that they may cause a problem like fire, especially when you place the wrong thing inside," she says.

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The good news is that you can easily avoid a kitchen fiasco by taking a moment to consider the food containers you are using. From styrofoam to metal, here are things you should think twice about before putting in the microwave. 

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1. Styrofoam containers 

Expanded polystyrene containers tend to leach chemicals when exposed to heat.

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Expanded polystyrene foam — more commonly known as "styrofoam" — is type of plastic that comes in many forms, from takeout containers to packing peanuts. While the FDA deems expanded polystyrene foam safe for food contact, and there are some polystyrene foam containers that are marked as microwave-safe, it's best to avoid putting styrofoam in the microwave altogether.  

"Even though these types of containers are commonly used to keep your food and drinks warm due to the insulation provided, Styrofoam doesn't react well to the high temperatures emitted by a microwave," says Ron Shimek, President, Mr. Appliance. "This could lead the material to break, melt, or release toxic chemicals that could mingle with your food.

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2. Plastic bags and containers 

Only microwave plastic products that are marked microwave safe.

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Microwaving plastics can cause chemicals to leach into your food or drink. Unless it's clearly labeled safe for the microwave, you should avoid microwaving any food in plastic. 

The two main chemicals that could leach out are phthalates and BPA, which are commonly added to plastic to make it flexible and pliable. Moreover, thin, single-use plastics and cold-storage containers — like condiment cups, butter tubs, and yogurt cartons — can melt in the microwave. 

It's worth noting that most plastic products have a number associated with them, typically displayed in a small recycling triangle emblem. You can technically use those numbers as a guide to understand what plastics are microwave-safe. As a quick guide, avoid putting plastics with numbers 1, 3, 6, or 7 in the microwave. Safer options are labeled 2, 4, and 5. 

Even still, it's better to be safe. Microwave-safe plastics usually have a marking indicating they are safe to use, so make it a habit to check for those symbols, Jones says. A microwave-safe symbol usually features three wavy lines, which indicate heat.

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3. Metal utensils and cookware 

Metal utensils and cookware absorb electromagnetic waves when heated in the microwave, creating a risk for fire.

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To understand why it's not a good idea to put metal in a microwave, you need to have a basic understanding of how microwaves work.

When you press the start button, an electron tube inside the microwave — known as a magnetron — generates electromagnetic waves. Those waves are absorbed by the water molecules in the food, producing the the high temperatures that heats everything up.

Metal is unsafe to put in the microwave because it does not absorb electromagnetic waves. Metals are conductive, so with enough heat, those waves become concentrated on the surface. 

"When microwaved, all metals, including utensils, cookware, and travel mugs can spark a fire," says Shimek. This also includes any objects with metal in it, like Chinese takeout containers with metal handles, dishware with metallic paint or trim, or any packaging with metal twist ties or staples.  

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4. Insulated travel mugs and bottles

Avoid microwaving reusable water bottles and mugs as they're usually made with stainless steel or plastic.

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It might seem like a good idea to heat up your coffee or tea straight in your travel mug, but this definitely should be avoided. Most travel mugs are made out of stainless steel or plastic. Travel mugs made out of ceramic are the only kind of mug that's safe to reheat. 

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5. Aluminum foil

Like all metals, aluminum and aluminum foil should not be placed in the microwave.

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As a thin form of metal, aluminum foil should not be put in the microwave. Aluminum foil will reflect energy, not absorb it, says Jones. Just like metal utensils, foil can spark, resulting in damage or a fire.

It also doesn't make sense to cover food in aluminum foil. Remember: Metal reflects microwaves away from foods, and generally would slow their heating. As the Department of Agriculture's Food and Safety Inspection Service (FSIS) explains it, food can't absorb microwaves if it's covered by aluminum foil. 

That said, the FSIS says aluminum foil in small amounts, for short times, could be safe. For example, you may want to use a small amount of foil to shield a portion of a food item to prevent it from overcooking. If you do this, make sure the foil is as smooth as possible and keep close tabs on cooking. 

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Additional reading:
Can I put a paper bag in the microwave?
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How to Choose the Right CNG Cylinder: A Comprehensive Guide
The Science and Art of Microwave Popcorn Bags: Popping Perfection at Your Fingertips
Things To Consider When Choosing Frozen Food Pouches
The Benefits of Watch Winders: Keeping Timepiece Excellence Alive

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6. Cardboard food boxes

Some cardboard boxed are lined with coatings or have metal hardware, so avoid placing them in the microwave.

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Plain cardboard takeout containers should be OK to microwave — check for the microwave-safe label. However, if the container is lined with waterproof coating of wax or plastic, or the box contains metal, skip the microwave. Provided it truly is plain cardboard—again, check for that microwave-safe symbol—you can microwave it for about 60 to 90 seconds only; otherwise, it will dry out and pose a fire hazard. 

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7. Brown paper bags

Paper bags cannot withstand the level of heat a microwave reaches.

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Some paper products like towels, plates, and bowls are microwave safe. Shimek says you should always use one of these to cover a container in the microwave to keep the contents from splattering.

However, paper bags are a different story. "Paper bags can't withstand the same level of heat and can emit toxic fumes or even catch fire, so avoid putting them in the microwave," says Shimek.

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What materials are safe to microwave?

Glass containers and reusable food containers are typically microwave safe.

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As mentioned, glass, ceramic, and plastics that are safe to use in a microwave will be labeled clearly. Here are some common materials you can use in the microwave:

• Glass: Glass is almost always microwave safe, especially heat-proof glass from brands like Pyrex. 
• Ceramics: Stoneware and porcelain dishware are generally safe for the microwave. Just avoid any dishware with metallic trim. 
• Reusable food containers: But generally speaking, containers from brands like Tupperware and Rubbermaid are safe to use in a microwave. But not all reusable food containers are microwave safe, so look for a microwave-safe symbol. 
• Paper plates: Plain paper plates can be microwaved, but watch out for any plates coated in plastic or with designs. 
• Plastic wrap. You can microwave plastic wrap as long as it's not directly touching the food. Otherwise, the wrap might melt into your meal.
• Parchment paper: This is safe to use in both a regular oven and a microwave. 

Best food storage containers

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We test and recommend the best food storage containers. Several of our favorites are microwave safe. Check out our picks: 

• Best overall: GlassLock 14-Piece Oven-Safe Box Set With Lids - See at Amazon
• Best multi-compartment containers: EasyLunchboxes 3-Compartment Lunch Box Containers - See at Amazon
• Best for large items: Lock & Lock Airtight Rectangular Food Storage Container - See at Amazon

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Insider's takeaway 

Nothing beats the convenience of a microwave when it comes to heating up food. However, you'll have a much bigger problem on your hands than cold leftovers if you use cookware not suited for microwave use. Be sure to check for the microwave-safe mark on all containers and exercise caution when taking heated items out of the microwave.

Barbara Bellesi Zito

Barbara Bellesi Zito is a freelance writer from Staten Island, NY. She covers trends in real estate and home improvement for a number of publications, including Apartment Therapy, The Motley Fool, and Angi/Home Advisor. Barbara also writes fiction, and her debut novel is forthcoming in 2022.

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Disposable paper cups should not be heated in the microwave oven, because some disposable cups use polyethylene coating instead of PE coating, which will produce harmful ingredients when heated.

Welcome to our comprehensive guide on microwave paper cups! Microwaving food has become a convenient and time-saving method for many people, but when it comes to using paper cups in the microwave, safety concerns often arise.

Whether you're a coffee lover who frequently heats their morning brew or someone who occasionally uses paper cups for reheating leftovers, this guide will equip you with the knowledge to ensure your microwave usage remains safe and worry-free.

Contents:

Part I. Understanding the Composition of Paper Cups

Part II. Potential Risks of Microwave Paper Cups

Part III. Factors to Consider Before Microwaving Paper CupsPart IV. Tips for Using Paper Cups in the Microwave

Part IV. Tips for Using Paper Cups in the Microwave

Conclusion

Part I. Understanding the Composition of Paper Cups

To understand whether it's safe to microwave paper cups, it's important to first grasp their composition. Paper cups are typically made from a combination of paper and a thin layer of plastic or wax. The paper provides the cup's structure, while the plastic or wax lining acts as a barrier to prevent liquid from seeping through. This lining also helps to keep the cup's shape intact, especially when it comes into contact with hot liquids. It's this plastic or wax coating that raises concerns about microwaving paper cups, as certain types of plastic are known to release harmful chemicals when exposed to heat. However, not all paper cups are the same, and the type of coating used can vary depending on the manufacturer and intended use.

Part II. Potential Risks of Microwave Paper Cups

While the plastic or wax lining in paper cups is designed to withstand hot liquids, microwaving them can still pose potential risks. One of the main concerns is the possibility of the plastic or wax coating melting and leaching into the food or beverage. When heated, the chemicals in the lining can transfer to the contents of the cup, potentially causing health issues if consumed. Additionally, the heat generated in the microwave can cause the paper cup itself to become hot, increasing the risk of burns when handling it. These risks are heightened when using paper cups that are not specifically labeled as microwave-safe. It's essential to be aware of these potential dangers and take proper precautions to minimize the risks.

Part III. Factors to Consider Before Microwaving Paper Cups

Before microwaving paper cups, there are several factors to consider. Firstly, check the cup's packaging or label to see if it is specifically labeled as microwave-safe. If it is not, it's best to transfer the contents to a microwave-safe container before heating. Additionally, consider the temperature and duration of microwaving. Higher temperatures and longer durations can increase the likelihood of the cup's coating melting or the cup itself becoming excessively hot. To minimize these risks, it's advisable to use lower power settings and shorter heating times. Lastly, always exercise caution when handling the cup after microwaving, as it may be hot to the touch. Use oven mitts or allow it to cool before handling.

Part IV. Tips for Using Paper Cups in the Microwave

If you choose to use paper cups in the microwave, there are some tips to ensure safe usage. Firstly, always check the cup's packaging or label to confirm it is labeled as microwave-safe. If it is not, transfer the contents to a microwave-safe container before heating. Secondly, avoid using paper cups with metallic accents or designs, as these can cause sparks and pose a fire hazard in the microwave. Additionally, be mindful of the cup's fill level to prevent spills or overflowing when the contents heat up. Lastly, allow the cup to cool before removing it from the microwave, as it may be hot and can cause burns. By following these tips, you can minimize the risks associated with microwaving paper cups and enjoy your food or beverage safely.

Conclusion

In conclusion, microwaving paper cups can be safe if the cups are labeled as microwave-safe and used correctly. Understanding the composition of paper cups, the potential risks involved, and the common misconceptions surrounding microwaving paper cups is crucial for making informed decisions.

It's important to choose a reliable and trustworthy supplier of disposable paper cups. Here are 5 key considerations to keep in mind when choosing a disposable paper cup manufacturer.

LOKYO offers a wide range of food-safe packaging solutions.

By considering factors such as the cup's labeling, temperature, duration, and safe alternatives, you can minimize any potential health risks associated with microwaving paper cups. Remember to always exercise caution when handling the cup after microwaving and follow the manufacturer's instructions. With this comprehensive guide, you can confidently navigate the world of microwaving paper cups and enjoy your favorite beverages or reheated meals without any worries. Stay safe and happy microwave.

For more information, please visit microwaveable bags for popcorn.