Microwave Marshmallow Experiment

Have you heard of the microwave marshmallow experiment? It’s really simple and a fun way to explore how the volume of gas expands a marshmallow as it heats up. My kids also enjoy this experiment because it mixes science (+ fun) with a sugary treat.

The fun and simple microwave marshmallow experiment | Tinkerlab

Microwave Marshmallow Experiment Supplies

  • 4 (or more) Marshmallows
  • Paper Towel or Microwave-safe plate
  • Microwave
  • Paper to jot down observations (I’ll share my 3-year old’s observations in italics below)
For this microwave marshmallow experiment, we’ll microwave three marshmallows for different periods of time, and then  compare what happens to the marshmallows as they heat up, and then cool down again. This is an engaging way to involve children in scientific observation and discovery, it raises lots of questions, and doesn’t require a lot of prep or clean-up. Are you with me?

Step One

Microwave one marshmallow for 10 seconds and remove from the microwave. Compare it to an uncooked marshmallow and describe how it looks. How does it feel?

The fun and simple microwave marshmallow experiment | TinkerlabObservation: It’s small, shorter than the other marshmallow, but fatter. It’s gooey.

The fun and simple microwave marshmallow experiment | Tinkerlab

Step Two

Microwave the second marshmallow for 30 seconds and remove it. How does it compare with an uncooked marshmallow? What happens to it as it cools?

Observation: It’s a little bit larger than the other one. It got dry as it cooled.

The fun and simple microwave marshmallow experiment | Tinkerlab

Touching the second marshmallow.

The fun and simple microwave marshmallow experiment | Tinkerlab

Cool, a little hole showed up in the middle after it cooled down a bit.

The fun and simple microwave marshmallow experiment | Tinkerlab

Step Three

Microwave the third marshmallow for 50 seconds and remove from the microwave. Compare to and uncooked marshmallow right away and after it cools. How are they different? How does this marshmallow feel?

Observation: It’s huge and wrinkly and dry. It’s brown. That means it burned. That means it’s good to eat. Crunchy to eat.

The fun and simple microwave marshmallow experiment | TinkerlabYou can see all three marshmallows here. We noticed that the 30 second and 50 second marshmallows got hard and crunchy as they cooled, and N decided to taste them for a flavor comparison.

The fun and simple microwave marshmallow experiment | TinkerlabThe 50 second marshmallow was brown, crunchy, and caramelized. Have you ever tried astronaut ice cream? It had a similar texture.

The science behind the activity is explained clearly over here at The Exploratorium. In essence, the volume of gas in the marshmallow increases when the temperature increases, and then decreases as it cools down. The Exploratorium suggests not microwaving marshmallows for longer than 2 minutes, less you want a dark, stinky, burnt mess on your hands.

This project was inspired by a book we found at the library: Kitchen Science Experiments: How Does Your Mold Garden Grow?

Have you ever microwaved anything and been surprised by the outcome?



  1. says

    this hit home when i saw it — when my sister and i were kids and we couldn’t find something sweet in the house to eat, we would stuff 3 chocolate chips inside of big marshmallows and put about 7 or so on a paper plate. we’d microwave it and watch them fluff up. after, we’d stir it all around with a fork and enjoy the melted chocolate with that “astronaut ice cream texture” you described. my mom was not a huge fan of this snack we “invented” (so we thought) but (shhh) i still make it to this day. ;)

    • Rachelle says

      That’s so awesome, Jen. I remember experimenting with food in the kitchen too, but nothing came out all that delicious. Just lots and lots of messy gooey concoctions. That’s funny that you still make it to this day. I can see the chocolate taking it up a notch!

  2. Lucy says

    I’ve microwaved colored CDs before to make jewelry (alas, they are now scant).  I also got the surprise of my life when my baked potato caught on fire.  Don’t ask me how….  I’m not safe around most kitchen eqpt!

  3. says

    Microwaving marshmallows has unintentionally become a tradition that the kids do each year at the cabin. They experiment with all sorts of concoctions…rolling marshmallows around nuts and microwaving, trying to stir melted chocolate and marshmallows together, etc.

  4. says

    thanks! we’ll definitely try this one this wknd., One thing I did (which is unrelated :) with my son a while back on a lazy saturday was “sink or float” – we basically collected things around the house and put them in a large jar of water and he would guess which one would, well, sink or float! Then we repeated it again in the bath later that night :)


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