Steve Spangler Science

Using a Purchase Order?  •  Back to School  •  Spangler Science Club

Questions? Give us a Call: 1-800-223-9080

Soap Souffle

Blow up a bar of Ivory soap in the microwave.

Rating: 54321

Submit A Review

The microwave oven is not just for warming leftovers. Grab a bar of fresh Ivory soap and gather your friends around the microwave oven. Sure, you could do it at your home, but save this great trick for the break room or the staff cafeteria. In under two minutes, you'll have the best soap soufflé you've ever seen.

  • Bar of Ivory soap
  • Various bars of another brand of soap
  • Deep bowl of water (or a plastic tub)
  • Paper towel
  • Microwave oven
Print Experiment


This experiment requires adult supervision and permission to use the microwave oven. 

Adult Warning! You will not be able to sneak co-workers into the cafeteria to see the incredible expanding soap trick without filling the office with the lovely smell of Ivory soap. Besides, the chorus of ooohs & ahhhs erupting from the cafeteria is a dead giveaway.

  1. Fill the bowl with water.
  2. Drop the bars of soap in the bowl of water. Notice how all of the bars of soap sink except for the Ivory brand soap. Why?
  3. Remove the Ivory soap from the water and break it in half to see if there are any pockets of air hiding in the middle of the bar. If there are, that would make the soap float, right? But there are no pockets of air. Hmm...
  4. Place the bar of Ivory soap in the middle of a piece of paper towel and place the whole thing in the center of the microwave oven.
  5. Cook the bar of soap on HIGH for 2 minutes. 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 souffle.
  6. 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.

What would happen if you microwaved a marshmallow? Try it! Put the marshmallow on a plate and microwave it for about 30 seconds. What happens? 

How Does It Work?

Ivory soap is one of the few brands of bar soap that floats in water. But when you break the bar of soap into several pieces, there are no large pockets of air inside. If it floats in water and has no pockets of air, it must mean that the soap itself is less dense than water.  Ivory soap floats because it has air pumped into it during the manufacturing process.

The air-filled soap was actually discovered by accident in 1890 by an employee at Procter and Gamble. While mixing up a batch of soap, the employee forgot to turn off his mixing machine before taking his lunch break. This caused so much air to be whipped into the soap that the bars floated in water. The response by the public was so favorable that Procter and Gamble continued to whip air into the soap and capitalized on the mistake by marketing their new creation as "The Soap that Floats!"

Why does the soap expand in the microwave?

This is actually very similar to what happens when popcorn pops or when you try to microwave a marshmallow. Those air bubbles in the soap (or the popcorn kernels or the marshmallow) contain water. Water is also caught up in the matrix of the soap itself. The expanding effect is caused when the water is heated by the microwave. The water vaporizes, forming bubbles, and the heat causes trapped air to expand. Likewise, the heat causes the soap itself to soften and become pliable.

This effect is actually a demonstration of Charles' Law. Charles' 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 quickly, causing them to move far away from each other. This causes the soap to puff up and expand to an enormous size. Other brands of soap without whipped air tend to heat up and melt in the microwave.

Customer Reviews

super fun Review by Holly Shea

this was a pretty easy thing to do for science fair ... and it was so fun.... and very interesting..... i recommend you try this for an easy A :)

(Posted on February 23, 2010)

Awesome Surprise Review by Patty

I have been entertaining my grandkids with Steve Spanglers Science for several years now. This experiment by far was the most hilarious and thoroughly enjoyed even by the adults when we recreated it for them. Thank you Steve Spangler for helping me be a fun grandma.

(Posted on April 30, 2011)

Ivory Soap Souffle Review by Lisa Carstens

Wanted to let you know we performed the experiment with Ivory, Dove, Dial and Irish Spring and they all rose except Dove.  the dove actually melted and kind of looks like grits.    your site says that most soaps won't expand but 3 of the four we compared did.  Now here are some photos...

(Posted on March 18, 2010)

Write Your Own Review

You're reviewing: Soap Souffle

How do you rate this experiment? *
1 star 2 stars 3 stars 4 stars 5 stars