Soap Soufflé – Microwave Soap Cloud Science Experiment

Blow up a bar of Ivory soap in the microwave.

What happens when you put a bar of Ivory soap in the microwave? Find out with Soap Soufflé, our fascinating soap cloud Ivory soap experiment. You’ll be shocked and awed at how easy it is to blow up a bar of Ivory soap in the microwave!
Ivory soap is known to be gentle and pure; after all, it’s the soap that floats. But why? With our microwave soap cloud experiment, you’ll discover the secret behind this floating sensation. How? By cooking the whole bar of soap in the microwave, that’s how!
That’s right: One bar of Ivory soap + the microwave oven = one very cool trick! Bonus: Your kitchen will smell so fresh and clean when you’re finished. Ready to blow up some soap? Let’s do this!
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Experiment Materials

  • Bar of Ivory soap (you must use Ivory brand soap)
  • Various bars of other brands of soap
  • Deep bowl of water (or a plastic tub)
  • Dinner plate
  • Knife
  • Microwave oven

Experiment Videos



The first part of this experiment is designed to prove whether or not the claim is true. Does Ivory soap really float? Fill the bowl with water and drop in a brand-new bar of Ivory soap. It’s a pretty simple test . . . does it float?


Maybe all bars of soap float. If you have other brands of soap, try the float or sink test. You’ll probably discover that all of the bars of soap sink except for the Ivory brand soap. Why?


Remove the Ivory soap from the water and break it in half to see if the bar of soap is actually hollow or if there are huge pockets of air. If either is true, that would make the soap float, right?


Use the knife to cut the bar of Ivory soap into four equal pieces. Place the pieces of soap on a dinner plate, and then place the whole thing in the center of the microwave oven, after asking permission from an adult.


Cook the bar of soap on HIGH for 1 minute. Don’t take your eyes off the bar of soap as it begins to expand and erupt into beautiful puffy clouds. Be careful not to overcook your soap soufflé.


Allow the soap to cool for a minute or so before touching it. Amazing. . . it’s puffy but rigid. Don’t waste the soap. Take it into the shower or bath. It’s still great soap with a slightly different shape and size.

How Does It Work

Ivory soap is one of the few bar soap brands that will float in water. However, when you break that bar of Ivory soap into several pieces, you’ll notice that there are no large pockets of air inside. So, if it floats in water yet has no large pockets of air, this must mean that the soap itself is less dense than water!
Why does Ivory soap float? It is because air is whipped into the soap during its manufacturing process. If you break the bar of soap in half with your hands and look closely at the edge of the bar, you will see tiny pockets of air. However, when you cut the soap with a knife, it leaves a smooth edge. (In other words, it’s impossible to see those exposed air bubbles.)
Ivory soap in a microwave expands because of a process that is very similar to what happens when popcorn pops or when you try to microwave a marshmallow. Those air bubbles in the soap (or in the popcorn kernels or in the marshmallow) contain water molecules. Water is also caught up in the matrix of the soap itself. When the water is heated, it causes an expanding effect. The water vaporizes and the heat causes the trapped air to expand. Likewise, the heat causes the soap itself to soften and to become pliable.
This effect is actually a demonstration of Charles’s Law. Charles’s Law states that as the temperature of a gas increases, so does its volume. When the soap is heated, the molecules of air in the soap move about quickly, causing them to move far away from each other. This causes the soap to puff up and to expand to an enormous size. Other brands of soap (without that whipped air) tend to melt when they are heated up in a microwave.
And now the entire kitchen smells like — you got it: cooked soap!

The Ivory Soap Origin Story
The air-filled soap was discovered accidentally in 1890 when a Procter & Gamble employee forgot to turn off his soap-mixing machine before he took his lunch break. This caused so much air to be whipped into his batch soap that it was nearly double in size! When the soap was formed into bars, the bars floated in water. The response by the public was so favorable that Procter & Gamble continued to whip air into its soap, capitalizing on the mistake by marketing their new creation as “The Soap that Floats!”

Take It Further

Try this same microwave soap experiment with different bars of soap. What happens? Do you see the same results? If you have an older bar of Ivory soap around the house, do a side-by-side comparison test between the older soap and a brand-new Ivory soap bar. Does the age of the soap have any effect on the size of the soap soufflé?
What would happen if you microwaved a marshmallow? What are you waiting for? Try it! Put the marshmallow on a plate and microwave it for about 30 seconds. What happens? Run the test several other times with new marshmallows and different “cooking” times.

Safety Information


This experiment requires the use of a microwave oven. Even though you’ve used a microwave oven a zillion times to heat your leftover burritos or spaghetti, our lawyers are making us include this warning: Adult supervision is required.

Steve Spangler Science: Fabulous Fun; Spectacular Science

If you loved this soap cloud experiment, there are more ideas for hands-on, kid-friendly science project instructions on our website! Don’t miss our library of online experiments — each provides a fascinating, visual demonstration of a scientific principle that can be done at home or in class. For science super fans, don’t miss the opportunity to sign up for the Steve Spangler Science Club, which sends you everything you need for a monthly at-home science experiment — Steve Spangler style.
What makes Steve Spangler Science different? It’s our WOW factor and our dedication to inspire those “ooohs” and “ahhhs,” which means that kids are getting excited about science. We aim to make our science experiments fun, memorable and entertaining for all ages. So, whether you’re looking for a good reason to put an Ivory bar of soap into the microwave, create a fluffy soap cloud or blow up a perfectly good skin cleanser, we can’t think of a better reason than to help you learn about science!
Note: Your Ivory soap in the microwave experiment may change the shape of that ordinary bar of soap and turn it into a fluffy cloud. Don’t throw it away, though. Use it in on your sink to wash your hands or in your shower to wash your arms and legs. It is still 100% effective at cleansing (even if it does look a bit like a marshmallow).

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