Marshmallows aren’t just for hot cocoa or s’mores—they’re also a super fun way to learn about air pressure! In this experiment, you’ll watch marshmallows magically grow bigger right before your eyes. The “puff-up” trick is simple, safe, and a great way to explore how invisible air all around us can affect even a squishy, sugary snack.

What You’ll Need

You only need a few supplies for this experiment:

  • A bag of regular-size marshmallows (mini marshmallows will work too, but the results are easier to see with bigger ones) 
  • A microwave-safe bowl OR a large clear cup with plastic wrap 
  • A microwave (option 1) or a vacuum pump/sealed container (option 2, if you have one) 

Step-by-Step Instructions (Microwave Method)

  1. Get Ready: Place one marshmallow in the center of a microwave-safe plate or bowl. 
  2. Heat It Up: Turn on the microwave for about 20 seconds. Watch carefully! 
  3. See the Puff-Up: The marshmallow will start to grow, doubling (or even tripling!) in size. 
  4. Cool and Collapse: Once you stop the microwave, the marshmallow will shrink back down again. (Careful—it will be hot!) 

Step-by-Step Instructions (Vacuum Method)

If you have a vacuum pump or a science kit with a sealed container, you can try this alternate version:

  1. Place the Marshmallows: Put several marshmallows inside the clear container. 
  2. Seal the Lid: Make sure no air can escape. 
  3. Pump the Air Out: As the vacuum removes air, the marshmallows puff up and expand. 
  4. Release the Air: When you let the air back in, the marshmallows shrink back to normal. 

The Science Behind the Puff

So, why do marshmallows expand and then collapse? It’s all about air pressure and gas molecules.

  • What’s Inside a Marshmallow: Marshmallows aren’t solid—they’re mostly sugar, water, and lots of tiny air bubbles trapped inside a fluffy structure. 
  • Microwave Version: Heating the marshmallow makes the air inside those bubbles expand. The heat also softens the sugar and gelatin holding the bubbles together, letting them stretch like balloons. 
  • Vacuum Version: In normal air, the marshmallow is “squeezed” by air pressure all around it. When you remove that air with a pump, nothing is pressing in on the marshmallow anymore, so the bubbles inside expand. 
  • Collapse: Once the marshmallow cools (microwave) or air pressure returns (vacuum), the bubbles shrink back down, and the marshmallow loses its giant size. 

Fun Variations to Try

Want to get creative with your marshmallow science? Try these fun twists:

  • Mini vs. Jumbo: Compare what happens with mini marshmallows, regular ones, and jumbo-sized. Which one grows the most? 
  • Shape Show: Try different marshmallow shapes—stars, twists, or holiday ones. Do they puff up the same way? 
  • Timing Test: Heat marshmallows for different times—10 seconds, 20 seconds, 30 seconds. How does the puff-up change? 
  • Squish Test: After microwaving, let the marshmallow cool, then touch it. You’ll notice it feels crunchy instead of squishy because the sugar structure hardened as it cooled. 

Real-Life Connections

This silly marshmallow experiment connects to some fascinating real-world science:

  • Air Pressure: Air is invisible, but it’s powerful. It pushes on everything around us, even if we don’t notice. 
  • Hot Air Balloons: Just like marshmallows, hot air balloons rise because the heated air inside expands and becomes less dense. 
  • Baking: Cakes, cookies, and bread rise in the oven for a similar reason—air and gases expand when heated. 
  • Space: Astronauts need pressurized suits because without air pressure, gases in their bodies would expand (kind of like a marshmallow in a vacuum chamber!). 

What You’re Learning

The Marshmallow Puff-Up teaches some awesome science ideas:

  • Air Pressure: How invisible air can keep things squished or let them expand. 
  • Gas Expansion: Heat makes gas molecules move faster and spread out. 
  • Physical Changes: Heating and cooling can change the texture of food. 
  • Observation & Curiosity: Watching carefully and testing different variables makes you think like a scientist. 

Safety Notes

  • Microwave Marshmallows Get Hot! Always let them cool before touching or eating. 
  • Don’t Overdo It: If you heat a marshmallow too long, it can burn and make a mess. Stick to short times. 
  • Vacuum Kits Only with Supervision: If you’re using a vacuum pump, always have an adult help set it up. 

Wrap-Up

Marshmallows may look like just a sweet snack, but they’re also packed with science. Whether you use heat or a vacuum, you’ll see the power of air pressure in action as those sugary treats grow and shrink before your eyes.

So next time you’re craving a marshmallow, grab a few extra and turn snack time into a science lab. The Marshmallow Puff-Up is proof that learning can be both sweet and seriously fun!