This incredibly simple science experiment only needs a bar of soap and your microwave. Give it a try and see a bar of soap expand to six times its size right before your eyes. Our students at CEFA Early Learning schools love it! At the end of this activity, I will show how to use the cloud of soap you have created in other fun ways.

Best Ages for This Activity

Two to five

How to Make It


You Will Also Need

  • A microwave
  • Any microwave-safe dinner plate
  • A way for your child to reach to the level of your microwave to observe

Let’s Get Started

  • Invite your child to try a science experiment.
  • Invite them to unwrap the bar of ivory soap, and encourage your child to use descriptive words to describe how it feels, how it smells, etc. Ivory soap has a higher air content, which makes it possible for this experiment to work. It has so much air in fact that it floats in water! (don’t try it with this bar, however – maybe another time).
  • Make sure your child can get a good view of the microwave, and help them place the unwrapped bar on a plate and bring it to the microwave.
  • Help them press the microwave timer for 2 minutes, and watch as the soap magically expands before their very eyes!
  • Once it is ready, remove the plate yourself as it may be hot, and wait until it cools off before your hand it to your child to examine.
  • Again, use descriptive words to describe how the soap changed.
  • The area surrounding your microwave will smell of soap but will not leave a soapy taste next time you use the microwave. The scent itself is a great sensory experience for your child. Describe how that changed too.
  • The soap will now feel fluffy, crumbly and powdery, and is so much fun to play with! Just make sure they don’t taste it!
  • Place your soap fluff in a sensory bin so your child can play. Offer cookie cutters, butter knives, and toys if you wish.
  • Be careful that your child does not touch their eyes or mouth with soapy hands.

The Science Behind This Experiment

The ivory soap bar floats and is very light because air is whipped into it during the manufacturing process. If you break the bar of soap in half (use your hands) and look closely (give your child a magnifying glass) you will see tiny pockets of air in it.

Why does the soap expand in the microwave? The air bubbles in the soap contain water molecules. When that water is heated in the microwave, the water vaporizes and that vapor trapped in the soap is what makes it expand. Likewise, the heat causes the soap itself to soften and become more pliable.

When the soap is heated, the molecules of air in the soap move quickly, causing them to move far away from each other. This causes the soap to puff up and expand to an enormous size.

Learning Opportunities

This is a thrilling S.T.E.M. activity where your child can see a chemical reaction as it happens. For better science learning, follow the steps of your scientific method with your child.

Extended learning opportunities

  • Try the same experiment using popcorn kernels instead. The exact same chemical reaction occurs.
  • Try it with a marshmallow for the same results.
  • Use your new fluffy soap cloud to play.
  • Use your new fluffy soap cloud in the bath – you can slide around the soap, then finally add water for an extra soapy, extra cleansing bath.

CEFA tip: Remember to let your child do as much of the process as they are capable of.

CEFA WARNING: This experiment requires adult supervision at all times.

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