Can You Microwave Tin Foil?

Q. Can you microwave tin foil? Sometimes I have a sandwich wrapped in foil, and it would be easier to just stick the whole thing in the microwave instead of removing the foil and finding a plate to hold the food. I’ve also noticed some frozen food has foil containers that they say are microwave safe, but I’ve always heard you shouldn’t put metal in the microwave?

tin foil

A. It is important to remember that what we call tin foil is actually usually aluminium foil. The name tin foil just comes from the fact that older versions of foil were made from tin. Most modern foil is actually aluminium instead of tin because aluminium does not tend to make the food taste metallic. However, both tin and aluminum foil are essentially super thin sheets of metal, so the answer is the same regardless of which version you want to use.

The short answer to “can you microwave tin foil?” is basically that you technically could microwave foil, but you shouldn’t. Keep reading to find out why exactly the answer is so vague.

To understand the reason foil can behave so weirdly in the microwave, it is necessary to know how microwaves work and how they react to metal. Microwaves work by making radio waves that are absorbed by water, fat, or sugar. Since most foods contain these ingredients, the microwaves are absorbed into the food where they make the atoms in the food move back and forth rapidly. This rapid motion turns into heat, so the food heats up.

However, metal does not absorb microwaves. Instead, it reflects them. This means that the metal and anything else below it does not heat up as rapidly. Unlike bigger chunks of metal, tin foil can be thin enough that a little bit of radio waves slips through. This leads to some fairly odd behavior. Unlike other types of metal in the microwave, foil in the microwave does not always cause problems.

The problem with foil in the microwave is that tiny currents of electricity flow over the metal as it tries to reflect the microwaves. This is not an issue for hefty pieces of metal like the walls of a microwave, but it is a concern for thin bits of metal like aluminum. The problem is that the electrical current running along the metal can cause sparks. When the sparks hit anything flammable, it is possible for something in the microwave to catch fire.

What does this all mean? Essentially, you do not have to worry that your microwave is going to instantly explode if you put foil in there. In the best case scenario, there will be absolutely no problem from using aluminum foil in the microwave. This is common enough that you sometimes see microwave cookbooks recommending that people shield wing tips and other easily-burnt parts of food with a little foil as they cook. If you absentmindedly left some foil in your microwave once and did not notice any fire, you do not have to worry that you have completely ruined your microwave.

Generally, there are less risks of sparks if you use new, smooth foil. Foil that has been wrinkled is more likely to cause arcing that makes sparks shower throughout your microwave. Sparks are also more common if the foil is placed less than one inch from the walls or if the foil comes in contact with a metal shelf or turntable in the microwave.

However, this does not mean you should start throwing all your aluminum foil wrapped leftovers straight into the microwave. Almost all major microwave manufacturers recommend that people avoid putting foil in the microwave. Fires are common enough that they are an issue. Even a small fire can be a problem when it destroys that sandwich you have been looking forward to eating. A bigger fire can end up damaging various parts of your microwave and essentially making it unsafe to use. In some cases, there have even been microwave fires that catch on other parts of the kitchen and end up causing major house fires.

Since aluminum foil can potentially cause problems, it is better to be safe than sorry. The few extra seconds you have to take to remove foil from leftovers before heating it is better than the hours you will have to take cleaning or replacing your microwave if it catches on fire.

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