If you place a non-microwaveable glass dish in the microwave, it could ruin both the food and the glassware. The container could also melt, break, and even damage your microwave. So, it’s always best to check carefully whether your dish is microwave safe before using it to warm up your next meal.
It’s safe to microwave glass that has a ‘Safe for Microwave Use’ label or a squiggly lines symbol on the bottom. Make sure you don’t microwave glass ceramics, colored glassware, or a glass container with any metallic or foil trims. You can also microwave most plastics and paper safely.
Let’s take a closer look at the safety of microwaving glass and which types of glass you shouldn’t microwave, so that you can warm up your food without worrying about damaging the dish or the appliance.
Is It Safe to Microwave Glass?
Most glass containers are completely microwave safe, and warming up food in them won’t result in any volatile chemical reactions. However, it’s still important to thoroughly check your glassware before you use it.
Some manufacturers directly inform you whether the glassware is safe to microwave or not. So, if you purchase a new plate, bowl, jug, or cup, make sure you take a close look at it and check for any microwave-safe symbols.
For example, most glassware has either ‘Not Safe for Microwave Use’ or ‘Safe for Microwave Use’ written on the bottom. Alternatively, you might also find this information on the product’s box. In the UK, microwave-safe glass containers have a symbol of squiggly lines on the bottom.
So, if you find these squiggly lines or a small image of a microwave on your glass container, then you can safely use it in a microwave. You can also opt for specific glassware brands that manufacture microwave-safe containers, such as Duralex, Corningware, Visions, Anchor Hocking, and Pyrex (on Amazon).
Which Type of Glass Shouldn’t Be Microwaved?
Some glass containers aren’t safe for microwave use because of their manufacturing process, the type of additives or chemicals in them, or simply because of the designs and decorations on them.
Along with containers labeled ‘Not Safe for Microwave Use,’ there are several other types of glass you shouldn’t microwave:
Glass-ceramics are usually not microwave safe. Since they’re designed with ceramic clay, the internal bonds change when they’re heated and cooled too quickly, causing them to crack or shatter.
Additives in manufacturing, such as the dyes used to add color to glassware, can make certain containers unsafe for microwaving. This is because when you microwave these glass containers, the chemicals convert and become hazardous, especially when the food is directly touching the glass.
Glass With Foil or Metallic Trims
Glassware with metallic trims, or even a slight foil trimming on the rims, can cause sparks in your microwave. While these sparks are dangerous on their own, they’re also incredibly dangerous when they come into contact with fragile materials, such as glassware.
Glass With Air Bubbles
There are also several other types of glass that aren’t microwave safe by design, especially those that still have air bubbles left after production. Make sure you never use such containers in a microwave, as these bubbles expand when heated, causing the glass to crack or shatter.
Things That Shouldn’t Be Microwaved
It’s important to note that there are also certain things you shouldn’t microwave, regardless of the type of glass involved. For instance, you shouldn’t microwave an empty glass container, or use glass to overheat butter or oil in the microwave.
Here are a few other things that aren’t microwave safe:
- Brown paper bags
- Styrofoam plates and cups
- Plastic wrap (unless it’s labeled microwave safe)
- Dairy containers
- Some plastics, except those marked ‘microwave safe’
This list isn’t exhaustive, but it will hopefully give you a rough idea of the types of things you should avoid microwaving.
How to Check if a Glass Product Is Microwave Safe
If your glass product isn’t labeled or you’ve thrown away it’s packaging, then you could conduct a quick experiment to determine whether it’s microwave safe or not.
However, keep in mind that you shouldn’t do this test if your glassware is built with glass-ceramics, has a foil or metallic trim, or is colored. The purpose of the experiment isn’t to test for any dyes or additives, but instead to avoid cracking or breaking your glass containers in the microwave in the first place.
Materials and Tools Needed
- A glass container that you’re trying to test, which we’ll call Glassware 1.
- A cup that you already know is microwave safe, which we’ll call Cup 2.
- Make sure there aren’t any labels on the glass container you want to check.
- Set the microwave to its highest setting. You can usually find this option in ‘Power Level,’ ‘Menu,’ ‘Power,’ or ‘Settings.’
- Fill the microwave-safe cup with water.
- Keep the glassware you want to check empty.
- Place both Cup 2 and Glassware 1 together in your microwave. If your glassware is so big that it takes up almost all of the space in your microwave, place the microwave-safe cup inside Glassware 1. Just make sure you don’t pour any water into the glassware itself.
- Microwave both Glassware 1 (empty) and Cup 2 (filled with water) for one minute.
- Carefully touch Glassware 1 and gauge how hot it is.
If Glassware 1 is hot, then it’s a sign that it isn’t safe to use in a microwave. This is because most microwave-safe glassware is only slightly warm to the touch when microwaved. If your glass container is cool, but Cup 2 is hot, then you can probably use your container safely in the microwave.
If you placed Cup 2 inside Glassware 1, then the small area where both pieces were touching might be hot. But if you feel that the general surface of your glass container is cool to the touch, then it’s probably microwave-safe.
What Other Materials Are Microwave Safe?
Most people aren’t aware of the fact that there are only a handful of materials that are microwave safe. For this reason, it’s always advisable to check your microwave’s manual and the label on your container before placing it in the microwave.
Here are some materials that you can safely use in a microwave:
You can safely use paper towels, wax paper, paper plates, parchment, and paper bowls in a microwave. However, avoid using recycled paper towels or those with any sort of printing on them, as they could result in a potential safety hazard.
Most plastic Tupperware — like this container set from Vallo (on Amazon) — is completely microwave safe. But if a plastic container isn’t labeled ‘Microwave-safe,’ then don’t put it in your microwave. Make sure you always check the warnings and label on a plastic item before placing it in your microwave as well.
It’s advisable to avoid using any single-use plastic containers with margarine, cottage cheese, or yogurt in your microwave. Melted or pitted and warped plastic containers aren’t a safe option either. And while you can microwave food that’s covered with plastic wrap, it’s important to ensure that the wrap isn’t touching the food.
You can microwave aluminum foil only if it’s shielding your food. Small, smooth pieces of aluminum foil that cover up pieces of meat or poultry are perfectly safe to use in a microwave. However, make sure that the foil is at least 2.5cm away from the microwave walls to prevent arcing (or sparks in the microwave).
If the foil is crumpled, bent, or in very small pieces, never place it in your microwave. If you do, then you’ll definitely experience some scary sparks.