Maybe you've brought some takeout home in a cardboard box that you had leftover or maybe you've had some delivered to your door but it's not quite warm enough. Can you microwave cardboard takeout boxes?
I had a look online and some people said you could and some people said you couldn't so I decided to actually put it to the test myself and to work out if you can microwave cardboard takeout boxes and exactly what it takes to make it dangerous and potential cause a fire hazard.
Here's what I found:
It is very safe to microwave cardboard takeout boxes. The cardboard will get hot but is highly unlikely to set fire unless scrunched up and put in the microwave without food or liquid. Avoid putting cardboard takeout boxes with metal handles in the microwave as these can set fire or spark more easily.
I've done a variety of experiments and set lots of things on fire in the microwave but when I tried heating up a cardboard takeout box nothing eventful really happened.
My Experiment: Microwaving a Cardboard Takeout Box
I wanted to see if I could set the cardboard takeout box on fire so what I did was I put it in the microwave empty for 2 minutes, then a further 3 minutes.
What I found was that a bit of a smell of burning came from the microwave but the cardboard box did not catch on fire.
However, it did get extremely hot reading as high as 163ºC (325ºF) when I took it out of the microwave.
This was done with no food in it which is more dangerous. Without having food or liquid in the microwave the energy is focused more onto the cardboard takeout box.
If the box had food in it then a lot of the energy from the microwaves would be absorbed by the food, meaning it would take longer to heat up the box as much as I heat it up.
Can Cardboard Takeout Boxes Set Fire In The Microwave?
In the experiment above with the cardboard takeout box I wasn't able to set it on fire within 5 minutes.
But I did noticed a slight burning smell and the cardboard did get extremely hot, hot enough to burn for sure.
So is it possible to set cardboard takeout boxes on fire in the microwave and if so how would this happen?
Well I took the experiment and made it even more extremely. I scrunched up cardboard and put it in the microwave on a timer for 5 minutes. You can see the results below or read my article on can you microwave cardboard:
After about 2 minutes the cardboard set on fire.
What I discovered was that cardboard that is flat gets hot but doesn't seem to set on fire in the microwave.
However, scrunched up cardboard does create extra hot spots and these can become hot enough to ignite and send the entire thing up in flames.
Because cardboard takeout boxes have folds and places where the cardboard overlaps this gives it the potential to have hotspots where the cardboard cold ignite.
But again this is very unlikely especially if you have food inside the cardboard takeout box as the food will absorb a lot of the microwave energy.
These were pretty extremely conditions I put these cardboard boxes in and there were a lot of tests where nothing even happened to them. Still they were fun to do.
See more microwave experiments:
Can You Microwave A Cardboard Takeout Box With a Metal Handle?
The cardboard takeout boxes with the thin metal handle pose an extra risk when placed in the microwave.
Metal heats up quickly in the microwave as I showed in my experiment on putting metal cutlery in the microwave and the thinner and smaller the metal the faster it can heat up.
Now for a spoon on the side of a plate this doesn't pose a huge risk and is usually going to be fine.
But for a tiny thin piece of metal with small pointy edges directly attached to a thin and highly flammable cardboard box, well you can imagine what might happen.
Sparks may or may not fly from the metal but all of that heat close to and focused on the cardboard that is already getting very hot by itself could cause the cardboard to burst into flames.
To make these takeout boxes safer to put in the microwave simply remove the little metal handle which isn't too hard to do.
Without the metal they are much less likely to ignite and much safer to microwave.
Can You Reheat Food In a Cardboard Box? What Are The Health Risks?
You would think that cardboard/paper takeout boxes would be safe to reheat food in.
We all know the dangers of plastic tupperware and take out containers leeching chemicals into our food and drinks and how BPA can potentially cause cancer.
But people are much less aware of the health risks with reheating food in cardboard takeout boxes.
According to Business Insider Australia a watchdog for evidence of PFAS, , a class of toxic chemicals linked to cancer, in paper to-go boxes and one sandwich wrapper product at Whole Foods Market.
A bit more research into PFAS and you find out that CNN have reported:
A growing body of science has found that there are potential adverse health impacts associated with PFAS exposure, including liver damage, thyroid disease, decreased fertility, high cholesterol, obesity, hormone suppression and cancer.
There is also this article from the United States Environmental Protection Agency warning us against the health dangers associated with PFAS.
But as a normal person we are going to have no idea if our cardboard takeout container contains these harmful chemicals or not.
From the research it seems unwise to reheat food in a cardboard takeout container, not because of fire hazard but because of potential health hazards from the chemicals in the cardboard.
So while you can reheat last night's takeout in the microwave in the original cardboard box it came in it might be a good idea to take it out of the box and put it into a glass or ceramic bowl instead.
Doing this you can avoid all fears of fires and you don't have to worry about the potential health hazards.