Looking for a fun and easy science activity to do at home with your kids. This microwave marshmallow experiment is a playful way to introduce young learner to scientific observation, cause and effect, and simple STEM concepts. The best part? It only requires a sweet treat that you probably already have in your pantry!
*Note: This experiment will require more help from an adult, as it involves using the microwave and the marshmallow can become hot.
What Happens When You Microwave a Marshmallow?
Kids are naturally curious, and this experiment taps right into that wonder. When you microwave a marshmallow, it expands and grows puffy. In fact, sometimes it might look like it will take over the plate!
Supplies
- Marshmallow
- Microwave
- Microwave-safe plate (recommended)
- Optional: Graham crackers and a Hersheys chocolate bar (Why not make s’mores when you have the main ingredient?)
Microwave Safety Tips for Kids
Before you get started, here are a few simple safety reminders to keep this experiment safe and fun:
- Always use the microwave with an adult (or the adult should manage this part) — Microwaves heat things up quickly! Grown-up supervision is important any time you are using heat.
- Use microwave-safe plates — Stick with ceramic or glass, never metal or foil (these ones can spark).
- Start with short times– Begin with 10 seconds and add time slowly. Marshmallows puff up fast and can burn if overheated.
- Never leave the microwave unattended.
- Be careful when taking the plate out of the microwave– It may be hot, so an adult should help with this part of the experiment.
- Let the marshmallow cool off before eating– The grown up helping with this experiment should always test if the marshmallow has cooled enough (no one wants to burn their mouth!).
Instructions
- Place marshmallow in microwave-safe plate.
- Microwave for 10 seconds and see what happens.
- Optional: Microwave for 5-10 more seconds and observe the changes again.
- Let cool before touching, it will be hot- at least 30 seconds!
- Talk about what you both saw and compare the marshmallow’s size and texture.
- Enjoy your tasty science experiment. (Or s’mores ☺️)
The Science Behind the Puff
Marshmallows are full of tiny air bubbles surrounded by sugar, gelatin, and water. When the marshmallow is heated in the microwave, the water inside starts to evaporate and turn into steam. As the steam forms, the air inside those little bubbles begins to expand. Since the sugar structure is soft and flexible, the marshmallow puffs up quickly, almost like it’s inflating!
Once you stop the microwave and the marshmallow begins to cool, it will shrink back down and become chewy. This is a fun (and tasty!) way to teach your child about how heat changes matter and the relationship between air, heat, and pressure.
Questions for Kids to Spark Curiosity
Encourage learning by asking questions:
- What do you think will happen?
- How did the size change?
- What happened when it cooled down?
- What would happen if we used a mini marshmallow instead?
Educational Focus of the Marshmallow Experiment
This simple STEM activity for preschoolers is more than just fun. It helps kids:
- Practice prediction and observation
- Understand cause and effect
- Explore how heat affects air and solids
- Build confidence in your scientists
Bonus Printable
Want to take this project a step further and turn it into a real science experiment? Download the free Scientific Method for Kids printable! It’s a great way to help little learners think like real scientists!
Experiment With a Twist
Is your preschooler having fun with this experiment? Pique more curiosity by microwaving two marshmallows at the same time? What happens to the space between the marshmallows? You could also try this experiment with a Peep marshmallow for spring time fun.
Final Thoughts
This sweet and stretchy science experiment is a fun activity to brighten up a rainy day or as part of a play-based homeschool science lesson. Microwaving a marshmallow is just one way that we can show our kids that learning can be fun, messy, and exciting!
Share Your Marshmallow Magic!
Tried this activity? We’d love to see your results!
Snap a photo of your marshmallow puffing up (or as part of a s’more) and share it on Instagram. Be sure to tag @smartplayforprek on Instagram, and use #SmartPlayScience.
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Want More?
Looking for more easy science activities for your kids? Check out some of the other experiments on the site:
