Tinfoil or tin foil (a misnomer) is a type of pliable cooking foil used to contain, keep warm, or insulate food. You can use it for storage or cooking of food as well as reheating of leftovers. Despite how it’s named, tin foil isn’t made of tin but instead of aluminum.
This is why it’s alternatively known as aluminum foil (in the U.S.) or aluminium foil (in the U.K. or Commonwealth English). It’s made of thin, pliable sheets of aluminum that you can wrap or end around objects or dishes.
It’s metallic wrapping paper. So can you microwave aluminum foil? If not, then why not?
Can You Microwave Tinfoil or Not?
No. However, it kind of is microwaveable in certain situations. If it’s absolutely not possible to microwave aluminum, then why do microwaveable hot pockets have containers lined with aluminum foil and whatnot?
In certain instances, microwaving aluminum is nearly as dangerous as microwaving a spoon or fork. However, certain exceptions also happen, like aluminum baking trays or aluminum found lining your hot pockets. It’s a bit of a crapshoot, for lack of a better term.
Because tin foil is metal and conducts electricity, the metal will tend to start glowing and burst into flame as soon as the microwave starts or is turned on. Crumpled foil is particularly bad since it’s through these sharp points where the radiowaves will travel.
You can microwave tin foil or aluminum foil covering your food as long as you keep it about 3 inches away from the metal walls and keep its edges rounded. Otherwise, don’t microwave it.
What is Arcing and How is Connected to Microwaving Tinfoil?
Arcing or electrical arcing is when the electric current from things like power cables or in this case, microwave radiation, flow through the air from a given conductive point to another. This manifests in aluminum foil in the form of sparks as well as electricity.
The light and heat energy from the arcing current is also known as “arc energy”. The magnetron of the microwave creating micro radio waves is basically using electricity and turning it into waves that affect the water molecules of food and beverages in order to heat them up.
When exposed to workers dealing with power cables, the arc energy can injure or kill them. When exposed to the interior of your microwave, it can possibly not affect it or destroy the whole devices by overheating or setting your food ablaze.
Sometimes—like in the case of accidentally leaving a spoon or fork inside your microwave—it’s better to err on the side of caution than to play Russian roulette with metal or aluminum inside the microwave oven.
Further reading: Can You Microwave Parchment Paper?
Why Does Microwaving Aluminum Sometimes Work without Sparks?
There are times when aluminum can cause sparks and times when it doesn’t. Let us explain. Some people think that tin foil causing fires is bogus because they’ve used a tin foil or aluminum tray to heat up pasta in the microwave before and it didn’t cause sparks.
The reason for this is that a certain set of circumstances must be met in order to induce arcing and sparks. For example, tinfoil that’s crumpled is more likely to cause sparks than the smooth tinfoil of an aluminum tray.
Aluminum foil is quite thin. There’s the foil that’s 0.2 millimeters or 7.9 mils in thickness. There are also thinner gauges like the 0.24 mils or 6-micrometer gauges of foil. Tinfoil this thin means the microwaves tend to pass through them like nothing.
The thinner the foil the likelier it is to develop hotspots or have superheated food melt its thin aluminum leaves. Sparks fly when the sharp points of conduction are closer together and the foil is too thin to withstand the radiation.
What Exactly Happens If You Put Aluminum Foil in the Microwave?
Arcing can occur when aluminum foil is microwaved. Additionally, the higher the wattage of your microwave, the likelier it is to cause arcing or sparks. There’s simply more energy spread out when you have a high-wattage microwave oven on hand.
Long story short, a thick aluminum foil tray inside a low-wattage 700-watt microwave is the least likely scenario for tinfoil to cause sparks. In contrast, the thinnest leaf of crumpled aluminum foil placed inside a 1.2-kilowatt microwave is most likely to spark up like a fireworks display.
This is because more energy is made by a kilowatt microwave versus a 700-watt microwave. As this extra energy interacts with the water molecules of the food and superheats it, the foil will also become hot by virtue of heat conduction.
Did you know that aluminum has a melting point of 1,221°F? A 1.5-kilowatt microwave can reach heat of up to 1,221°F and higher, thus setting your tinfoil (and your food) aflame with sparks and electricity. Superheating food can reach such temperatures as well.
Sharp Edges versus Smooth Edges
Aside from thin tinfoil leaves and high microwave wattage, another factor that can influence the likelihood of sparks flying when you microwave your tinfoil wrapper is whether or not you crumple the aluminum like paper.
A crumpled wad of tinfoil is likelier to cause arcing and sparks compared to a smoothened out layer of aluminum, like in the case of aluminum trays or the tinfoil lining the inside of a hot pocket (one of the most microwaveable food items out there).
This is because the sharpness of the foil when crumpled allows electricity more leeway to travel from point to point. The conductive points of crumpled aluminum are more numerous compared to the completely smooth (and thick) aluminum used in aluminum trays.
Rounded edges allow conductive points to be further away from each other, thus the risk of arcing is lowered considerable. The sharp edges of crumpled aluminum make those sparks happen. This is also true of crumpled aluminum trays.
In a Nutshell
Have you ever eaten pop tarts? Have you opened a pack of it and placed them in the microwave to heat them up like hot pockets? If you’ve done that then you’ve surely seen arcing in action! It’d be like the Fourth of July in there.
Regardless, you should keep in mind that sparks and electrical arcs tend to happen to thin leaves of aluminum foil that’s all crumpled together. It’s less likely to occur with a thick aluminum tray for pasta but the risk is still there.