Halloween Marshmallow Science Experiment

Today we have a fast, simple and oh so fun Marshmallow Halloween Science Experiment for your kids. This kitchen science project has huge wow factor as students learn about the expanding power of heat. It also brings in some art for your artistic kids.

Halloween Science with Marshmallows

Halloween Marshmallow Science Experiment

Disclaimer: This article may contain commission or affiliate links. As an Amazon Influencer I earn from qualifying purchases.
Not seeing our videos? Turn off any adblockers to ensure our video feed can be seen. Or visit our YouTube channel to see if the video has been uploaded there. We are slowly uploading our archives. Thanks!

Many years ago we stumbled upon this simple and fun science experiment that my kids created after making some edible playdough.

See when you put a marshmallow in the microwave it expands and grows really big!

Although we did the original of this experiment many years ago, the kids still remember it and talk about the crazy huge marshmallows they created.

So we had an idea… what if we bought some jumbo marshmallows and did a Halloween version?

It was spookily perfect!

Halloween Marshmallow Science Supplies

Jumbo Marshmallows (we used Orange and White ones)
Food colouring and Paint Brush or… Food safe markers!
Paint brush
Microwave safe plate


Decorate your marshmallows. We used food colouring and a paint brush because that is what I had on hand, but if I was planning ahead for this activity I totally would have bought some food safe markers. The kids love using those markers and they can really get creative with their designs.

We drew pumpkin faces, ghosts and regular faces that turned into zombie faces (this is where it would have been good to have some markers so we could have easily used some green!).

Decorate marshmallows

Once you have your marshmallows designed, set it on a plate. Try to tip it ever so slightly backwards, as we found if we didn’t, as they expanded they sometimes tipped forward onto their faces and we couldn’t see the amazing distortion of the designs.

Set in microwave

Set the plate in the microwave and turn it on for 15 seconds. Watch closely!

You will see how it grows and grows and GROWS!

Halloween Marshmallow Science

When the microwave stops and you remove it from the microwave it will very quickly deflate. But you will be left with some spooky, fun distortions of your artwork.

Pro-tip! If you leave it in the microwave for too long, it will rupture and the effect will be lost. Test your microwave to find the perfect length of time. In ours it was about 15 seconds.

overheated marshmallow ghost

So now, why does this happen?

Marshmallow Science Experiment – The Science

This part is soooo cool! Let’s learn the science behind why marshmallows grow so big in the microwave.

Marshmallows are made with a whole lot of sugar, water and air bubbles. You can check out how to make your own marshmallows at home as a supplemental activity with this one.

When you heat marshmallows in a microwave the water molecules vibrate very quickly which makes the water heat up. This in turn warms the sugar (causing it to soften) and warms the air in the bubbles.

Since the warm air is trapped in side of the marshmallow bubbles (think of those marshmallow bubbles like little balloons), the heated air molecules get excited and move around faster, pushing against the marshmallow walls. With the warmed sugar softened, the hyperactive air molecules push and stretch the sugar. This makes it puff up.

If it puffs up too much, some air bubbles burst, and the marshmallow ruptures. Once the marshmallow starts to cool it deflates like a popped balloon. This made it very difficult to get good pictures. So I apologize now that I didn’t get any REALLY BIG marshmallow pictures. By the time we got them out of the microwave, they were already deflating.

This is a fast and super fun Halloween decorating activity to do with the kids, that has a cool science lesson. Explore more educational Halloween activities in our 31 Days of Halloween STEM Activities resource. It is packed full of spooky inspiration.


Halloween Activities
This simple marshmallow science experiment is an engaging STEAM activity for elementary. Learn a little science and a little art, then eat the results!
Hexagon STEM Build