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How Do You Know A Glass Or A Mug Is Microwave Safe?

A microwave is one of the most useful objects you can have in your home. You can use it to cook meals quickly, without needing to preheat your oven or learn any special cooking techniques. 

Microwaves can make a whole range of different dishes, so you’re not limited to just TV dinners – omelets, pasta dishes, and even some types of cake can be achieved with just a microwave for heat.

You can also do simple tasks such as melting chocolate or reheating leftovers in your microwave.

One thing you need to be careful about when microwave cooking is using only containers that are safe for that purpose. While most mugs, glasses and other receptacles are fine to use in a microwave, there are still some that aren’t. 

You shouldn’t use any container in a microwave that isn’t specifically microwave safe, but it can sometimes be difficult to know for sure. Here, we let you in on some handy tips and ways to find out if a certain cup is suitable for microwave usage or not.

Find Out If Your Container Is Microwave Safe

A lot of the time when you purchase a new item of kitchenware, it will say somewhere on the packaging that it is microwave safe. Look for instructions or smallprint, probably on the back of the pack it comes in. 

However, even if it doesn’t specifically state it, that does not necessarily mean that it is unsafe for that purpose. You may see a small microwave symbol instead of words, that is a shorthand way of letting you know that you can put it in the microwave.

Some things will come without any packaging, so there is nowhere for such instructions to be printed. Instead, there should be a symbol on the actual body of the container, usually on the bottom. 

Again, this will not be true of every single piece of kitchenware that is fine for microwaving, but it can help you to tell at a glance if it is.

Is there a way of telling that your container is microwave safe, even if it doesn’t have any indication that it is? Fortunately, there is something you can do to find out before you risk cooking any food in it.

Microwave Test

To check if a certain container is microwave safe, you can use this simple test. Find a cup that is definitely okay for the microwave and pour water into it until it is ¾ full.

Put both the container you want to check and the cup of water in the microwave, either side by side or one on top of the other.

Start the microwave on high and let it run for one minute (refer to the instruction manual if you don’t know how to adjust the settings for high power). After this time, take both items out of the microwave. Place your hand on the container to feel its temperature. 

If it feels hot and the water in the cup is cold, this means it is not microwave safe, because it has absorbed the heat. It is only safe if it feels cool and the water is warm. 

What Happens If I Use A Glass Or Mug that Isn’t Microwave Safe?

The possible consequences of microwaving a non-microwavable container will depend on the material it’s made from. Non-microwave safe plastic can melt and become deformed by the high temperatures required for heating the food properly.

If you then try and remove it, you can burn yourself on the molten plastic and it might even stick to you or the microwave. 

If you put unfired ceramic into a microwave, it can also melt because it isn’t yet able to withstand high temperatures. Another danger from this is cracking, in which case you could get small pieces of pottery all over the place. 

However, the biggest problem with microwaving this sort of ceramic container is that it contains toxic silica that can seep into your food.

When pottery gets fired, a barrier is created between the material and whatever it is holding, so no contaminants can touch the food.

Which Materials Are Most Likely to be Microwave Safe?

Most kitchen crockery, including plates, bowls, and mugs, is fine to use in the microwave as long as it has been glazed.

Plastic containers such as cups, tubs and pots are usually safe as well – indeed, microwave meals and takeaways often come in plastic pots that you can use to heat them up in.

You can’t assume that any plastic container you find will automatically be microwave safe, but ones that are food-safe should also work in a microwave.

Metal of any kind should never be placed in a microwave. Although people are generally familiar with this rule, it can be easy to forget when you’re in a hurry.

Luckily, kitchenware isn’t often metallic, but you should still take care not to accidentally put a saucepan in the microwave, for example. 

Another thing to be aware of is the fact that some plates or bowls etc. will have metal embellishments round the edge – these will make them unsafe for your microwave. Only use plain plates or ones you can be sure don’t contain even small amounts of metal.

Wooden containers are not recommended for microwaving either, because they contain small amounts of water so the heat can cause them to shrink.

Not many dishes are made of wood, but you do often get wooden utensils (e.g. wooden spoons), so you should endeavor to keep these out of the microwave.


Most of the time, any item of kitchenware that is microwave safe will tell you so, either on the outer packaging or on the container itself. If it doesn’t, you can use the microwave test to check if it is safe for heating food with.

It is a good idea to keep microwave safe containers separate from ones that are not microwave safe, so you don’t accidentally get confused and use the wrong one. 

You can label any that don’t explicitly say that they are microwave safe with a permanent marker pen, by drawing a symbol on the underside of the container.

This way, you won’t have to waste time checking again when you could be enjoying your microwaved food!

Jess Smith

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