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Can you boil water in a Styrofoam cup in the microwave?

How to Boil Water in A Microwave

Boiling water in the microwave is not the most complicated process in the world, but there are some important steps and things to check along the way. This will ensure that you are staying safe when completing this process. Microwaves, regardless of wattage, have the ability to make items incredibly hot, posing the risk of burns and fire damage.

Here you’ll find the steps you should take to boiling water in a microwave in a safe and contained way for quick and effective results.

  1. Pick A “Microwave Safe” Container

You will need a container in which to put the water in to boil. This container needs to be safe to put in a microwave, like this one here, which means that there is risk of damage to the microwave, the contents inside the container, or the container itself. These containers should not have lids as built-up steam can be dangerous and cause an explosion.

You are probably wondering which containers are deemed safe in the microwave. Here is a convenient list of the containers you can and cannot use when trying to boil water in the microwave. Paying attention to these items will allow for successful boiling and prevent unsafe materials from entering your water.

Containers Deemed Safe

These containers will have no issues in the microwave, but be aware that they may be hot when you remove them:  

  • Glass and ceramic dishes
  • Wax or parchment paper
  • Paper plates
  • Paper towels and napkins
  • Anything labeled microwave safe*

 *On many containers and dishes, it will say “microwave safe” on the bottom. If this is there on items in question, you can put it in the microwave. You should be aware that if the item is not made of one of the materials listed above, it is slightly riskier (especially if it is plastic).

Containers That Are Not Safe

You should not put these items in the microwave as they are typically not as durable or may cause fires and other problems:

  • Aluminum Foil – You should keep any metal away from the microwave to be safe. Aluminum specifically can cause fires or damage the microwave by creating sparks.
  • Dishware with metal or paints – Metals and metallic paints should also be avoided for similar reasons to those presented with aluminum.
  • Cold-storage plastic: These include the containers that you keep cottage cheese or butter in. They are made of toxic plastics that can be harmful if they melt or burn.
  • Brown paper bags – The thin paper can catch on fire and emit toxins.
  • Sealed containers – Lots of hot steam can cause the seal to burst off, creating a mess and potential damage.
  • Plastics – Try to avoid most plastics in the microwave. Tupperware and similar containers may be okay but usually are not the best because the chemicals from these items can seep into food. If it is deemed “microwave safe” you can use it.
  • Styrofoam – The only Styrofoam containers you should use are those noted as “microwave safe.” Styrofoam has chemicals that can be toxic as well but unlike may claims that it is always unsafe, some can be microwaved.
  • Plastic wrap – Some are deemed microwave safe, but as a general rule, try to avoid putting this in the microwave.

Try to avoid these materials if you can, especially when boiling water as you will be microwaving for a longer period of time than heating up smaller foods. The longer cook time presents greater opportunity for melting or burning of these materials.

We will dive into more detail about microwave safe items and more general safety later in this article!

  1. Pour Water into Container

Now that you have chosen the container you will use to boil the water, fill your cup or bowl with the desired amount of water you want. There are a couple of things you should be aware of when filling the cup for safety and practicality:

  • Do not fill to the ledge – When water boils, bubbles will arise. This may cause the hot water to spill over the edge and give you something to clean up once you are done.
  • Water level may decrease – Boiling water emits steam, and this will mean that some of the water is evaporating. If you leave the water in the microwave for too long, it could not only risk superheating (water reaches temperature above boiling point and may lead to explosions), but also give you less water than you wanted.
  • Do not seal container – As mentioned, you should not keep a seal on the container because it will lead to trapped steam that may cause an explosion and either damage the microwave or the container you are using.

If you avoid these issues, pouring the water into the container is very simple. It is suggested that you also put a microwave safe object into the water. This should be an item that does not contain any of the materials indicated on the “unsafe” list above. Wood is your best choice. This could be a wooden spoon or a popsicle, for example.

The reason you put something in the water is that if your water goes past the boiling point, it may not have something to form bubbles on in the water. Giving a microwave safe item for it to make bubbles on will prevent this overheating. Containers with chips or cracks can also replace the item and act as the area for bubbles to form.

  1. Put Water in the Microwave and Cook

Place the water in the center of the microwave plate as this will help to boil the water as evenly as possible from all sides. For most microwaves, it should take between 1-3 minutes to boil water. This is largely dependent on the wattage of your microwave. If you know the wattage, this is a general breakdown of how long it will take to boil water.

These are based on one cup of water. If you plan to boil more than one cup, you should expect boil time to be longer:  

  • 1,200 watts: 1.5 minutes
  • 1,000 watts: 2 minutes
  • 800 watts: 2.5 minutes
  • 700 watts: 3 minutes
  • 600 watts: 4 minutes

If you do not know the wattage, it is usually included in the owner’s manual, on the inside of the microwave, or on the back. You can also see how long it takes to boil one cup of water to determine the wattage for future cooking.

It is recommended that you boil water in intervals, not allowing cook time to exceed over 1.5 minutes with each pause. This will prevent superheating as steam starts to form. You can stir the water in each of these intervals and continue to cook until the desired time has been reached. Boiling water in the microwave does not produce obvious bubbles like on a stove.

Boiling points are lower at altitude. For every increase in elevation by 500 feet, the water’s boiling point is decreased by 0.9 Fahrenheit (or 0.5 Celsius). If you live in areas at higher elevation, you can expect the time it takes for your water to boil to be less.

  1. Safe Removal

Once you have successfully boiled the water, you must now remove it safely from the microwave. This is important as most containers that are microwave safe will still be very hot once the water has been boiled. You should take precautions when removing this container so that you do not burn yourself.

If you want to use the water while it is boiling, you will want to remove it when it is still very hot. Consider using an oven mitt or cloth towel to protect your hands upon removal. This will allow you to carefully take something out of the microwave without burning yourself on the container itself or the hot contents that could spill over.

Keep your face and skin away from the container right after heating as the steam is very hot, and there could be a chance of explosion from superheating. The most important thing to do when removing something from the microwave is to protect your body. Taking the necessary precautions in this somewhat dangerous endeavor can easily be made safe with attention.


How do you keep water from boiling over in the microwave?

You can either stop the microwave half way through the cooking process, give it a stir then continue cooking, or pour the ingredients and water into a larger bowl before microwaving.


  • NO PEEKING, NO STIRRING! Do not lift the lid or stir the rice while it’s cooking. That’s the surefire way to ruin it! Lifting the lid releases the steam = undercooked / unevenly cooked rice. Stirring = activates starch = gluey rice (this is the worst!).

  • NEVER skip resting for 10 minutes – this is when the rice finishes cooking in the residual heat and the water on the surface of each grain is fully absorbed, leaving you with perfectly fluffy, never gluey rice.

  • Don’t bring to heavy BOIL – for stovetop rice, don’t bring it to a rapid boil because then it’s so hot, when you put the lid on it will trap in so much heat it will probably boil over. Just bring it to a simmer/gentle boil on medium high (see video!) so there’s big gentle bubbles on the surface and it gets a bit foamy. You may still get a bit of liquid boil over if your lid isn’t heavy enough – if this happens, just add 1 tablespoon extra water next time!

JUMP TO Video | Recipe

JUMP TO Video | Recipe

How to cook rice in the microwave

Useful emergency method! I use this when I’m scrambling for rice props in photos!

  1. Place 1 cup of rice and 2 cups of boiling water in a microwave proof round^ container that’s 3 to 4 times taller than the water level (the water bubbles up quite a lot);

  2. Microwave uncovered for 12 minutes on high;

  3. Remove from microwave, cover then rest for 10 minutes;

  4. Fluff and enjoy!

* Most microwaves heat things from the outside in. Using boiling water helps rice cook more evenly.^ Round container cooks more evenly than square or rectangle, but not critical.

JUMP TO Video | Recipe

JUMP TO Video | Recipe

Cooking rice in the microwave is just as fast as using the stove, but it’s more hands off. BUT microwave rice is not quite as good as cooking rice on the stove. The rice doesn’t cook quite as evenly, but the difference is marginal and I’m pretty sure only rice snobs can tell the difference!

You might turn your nose up at the thought of microwave rice… but it’s super handy to know how!

When I’m cooking on the job and need rice fo

When I’m cooking on the job and need rice for stir fries or curries or something else I’m shooting, rice gets made in the microwave more often than not – for sheer convenience. Things get pretty hectic around here on shoot days!

Here’s a look at the rice cooked in the microwave. Hard to capture the texture in photos, but it is fluffy and doesn’t have that unpleasant gluey surface on the grains. You can see it better in the recipe video below!

JUMP TO Video | Recipe

JUMP TO Video | Recipe

Risks of Boiling Water in Microwave

There is a need to emphasize the danger of water reaching superheated temperatures when boiled in a microwave oven. At superheated temperatures, water becomes unstable. In other words, you face risks whenever you are boiling water in the microwave.

Some scientists at the University of New South Wales have discovered that one liter of water, superheated just by one degree, can produce around three liters of steam.

If you use a one-liter container to boil one liter of water in the microwave, water will explode out of the container when it becomes superheated. There have been reports of such incidents where people got injured.

Usually, water boils at 212°F (100°C) in an average domestic kitchen with bubbles and steam that emit from the kettle. However, the heat inside the microwave oven is generated by microwaves acting directly on the water molecules. Thus, it makes the water hotter than its container.

It is not like the heat generated by heating filaments in an electric stove or the gas in a gas stove. In the traditional way, the container is heated by filament or gas, and the container transfers its heat to the water. Then, the water boils when it reaches its boiling point.

Admittedly, such a process takes much longer than boiling water in a microwave. But there are also risks involved if you do not follow the recommended safety guidelines. Microwave-safe dishes and containers are typically smoother than saucepans and kettles. So, they don’t have nucleation sites.

Air bubbles have no places to cling to, unlike the rougher surfaces of ordinary kettles and pans. Also, boiled water in the microwave does not bubble and becomes unstable. So, when boiling water in a microwave, you really have to be careful and follow the safety guidelines.

Safety Precautions for Boiling Water in Microwave

The primary risk you face when boiling water in the microwave is that it may reach superheated temperature. It can cause superheated water to explode violently out of the container. Moreover, boiling water in a microwave does not usually produce bubbles. But when it is suddenly disturbed, it may create an explosion because of the lack of nucleation sites.

Also, when water is superheated, its temperature goes way above its boiling point. But if you use the proper container or observed the right safety precautions, it will not explode. To avoid accidents, here are some things you should do:

  • Don’t use oven-safe containers, pans, or dishes that have perfectly smooth surfaces. They don’t have nucleation sites where bubbles can form. If the boiling water is disturbed, it may explode, and you will have a mess on your hand.
  • Use older oven-safe containers that have some small scratches or little imperfections on their inner surfaces. These imperfections will serve as nucleation sites where bubbles can form.
  • Put a wooden stirrer or any oven-safe stick or utensil in the pan or dish. This stick will serve as the nucleation site of the molecules of the boiling water.
  • Use hot pads or wear thick kitchen mittens to hold hot pans.
  • Don’t touch the water to see if it is already boiling. Boiling water in a microwave usually does not produce bubbles. Don’t be tempted to check if it is boiling by touching it.
  • When boiling water in a microwave, do it in intervals. Don’t allow cooking time to go more than 1.5 minutes on every interval. Follow this method to prevent boiling water from reaching superheated temperature as steam begins to form. For each interval, stir the water and continue cooking until the estimated time is up.

Things to know about boiling water in a microwave

As mentioned, stirring water after boiling above the normal boing point can lead to an explosion. Here are the things you need to know when boiling water in a microwave to avoid any issue moving forward.

  • Check time: Water will not be superheated if you microwave in moderation. Although this depends on the amount of water heated, it is always safe to heat 30 seconds to one minute and stir.
  • Keep smooth heating cups or containers: Consider using older or rough cups and/or containers that are microwave-safe. These have cracks, marks, and stretches that help creates bubbles and prevent superheating.
  • Confirm boiling point: Always employ a cooking stick or long tool to confirm if the water is superheated. Simply test this by gently introducing the stick to the side of the cup/container. If you hear a burst noise, it will spill inside the appliance; hence you will prevent from injuries.
  • Don’t wait for long to stir: Stirring water occasionally in the microwave will help to avoid superheated water. If the water boils without spilling, then it is safe to use.
  • Wear protective gear: Protection is always better than a cure. Wear and prepare water protective gear such as gloves just in case the water spills on you or the exterior of the cup is scalding hot.

How long do you microwave water to boil?

In order to boil a cup of water in the microwave, the required time is approximately 1-3 minutes to reach the boiling point. However, this depends on the microwave wattage or amount of water being heated. 

The standard rule of thumb to boil a single cup of water in the microwave:  600 watt will take 4 minutes700 watt takes 3 minutes800 watt takes 2.5 minutes1000 watt takes 2 minutes1200 watt takes 1 minute.

Depending on the specific power setting of the microwave, it may differ the cooking time. The lower watt the machines has the more time you need to boil and the higher watt the machine provide the less time require water to boil using the microwave method.

Is it dangerous to boil water in the microwave?

Boiling water in the microwave is convenient and safe. The method is best used when heating small quantities of water, as microwaves can distribute heat unevenly. According to current research, no negative health effects are associated with boiling water in the microwave.