Growing and Shrinking Marshmallows

Vacuum packing Peeps marshmallows is an incredible (and delicious) demonstration of air!

A vacuum packer is an amazing device that vacuum packs food to seal in the freshness. At least that's what those late night infomercials tell us. We're more excited about using this fascinating device to explore the amazing properties of air pressure. Fill the special storage container with marshmallows (we prefer those adorable yellow Peeps) and remove the air. Watch out! It's the incredible growing marshmallow trick!

Experiment Materials

  • A kitchen vacuum packer from your local department store (Foodsaver or Black & Decker FreshGuard devices work well)
  • A vacuum packer storage container
  • Marshmallows of various sizes and types(Marshmallow chicks and bunnies are the best)


Not many kids have their own kitchen vacuum packer, so it goes without saying that adult supervision is required. Hey kids, you'll have to fight for time with the vacuum packer machine after Mom and Dad figure this one out! Be sure to read and follow the manufacturer's directions for using your specific kitchen vacuum packer.

  1. Fill the storage container jar with marshmallows and replace the lid.
  2. Attach the special vacuum hose that came with the unit.
  3. Place the hose over the vacuum port on the lid and start the vacuum packer.
  4. Don't take your eyes off those marshmallows! Why are they getting so big? When the unit turns off, remove the hose and stare at the marshmallows in amazement.
  5. Make sure everyone is watching when you release the vacuum. Watch as the marshmallows shrink when the air comes rushing back into the container.

Now that you understand the concept, try using a small balloon in place of the marshmallows or fill the storage container with soap bubbles. What would happen if you placed a small bag of potato chips into a large storage container and removed the air? Let's say the goal was to shrink the marshmallows – how would you do it? Place the marshmallows into one of the plastic storage bags that came with the vacuum packer. When the air is removed from inside the bag, you get to see the power of the air in the atmosphere as it compresses the marshmallows. Also see the Marshmallow Masher experiment.

How Does It Work?

The job of the vacuum packer is to remove the air from inside the storage container. Under normal conditions, molecules of air from the atmosphere (called atmospheric pressure) are pushing on the outside of the marshmallow. When the vacuum packer removes the air that was once pushing on the outside of the marshmallow, the air trapped inside the marshmallow pushes out (expands) causing it to get larger. The marshmallows shrink when the vacuum seal is broken and air rushes back into the container.

Please note that no marshmallow chicks were harmed while conducting this experiment… except for the Peep that we bit the head off of… that one didn't make it.

Additional Info

Thanks to Patti Duncan from High Point High School in Sussex County New Jersey for sharing this idea.