Expanding Ivory Soap Microwave Experiment

The Ivory Soap Microwave Experiment is one of the coolest science experiments for kids. All you have to do is put ivory soap in the microwave and watch it grow!


I bet never in a million years you thought about throwing a bar of soap in the microwave and cooking it. After all, soap is for washing our hands and body, not for eating!

Ah, but soap is also for science experiments. And in this case, we are going to use a specific brand of soap – Ivory soap.

I will explain why we use Ivory soap versus other brands later. For now, just trust me, use Ivory soap – not any other brand – for this experiment. Or else be ready to face one disappointed kid.

How to Grow Ivory Soap in the Microwave


  • Bar of Ivory soap
  • Microwaveable plate (grab the biggest plate you have that can fit in the microwave)
  • Microwave
  • Optional: an additional bar of Ivory soap
  • Optional: Any other soap bar from another brand
  • Optional: a bowl of water


  1. Optional: If you do have an extra bar of Ivory soap, try dropping it into a bowl of water. The Ivory bar should float. Drop the non-Ivory soap bar in the water. Any other soap bar besides Ivory should sink.
  2. Place the bar of Ivory soap (use a new, dry one if you did step #1 above) in the middle of a plate.
  3. Place the soap bar and the plate in the microwave.
  4. Cook the bar on HIGH for 2 minutes. 
  5. Watch the soap bar as it starts to grow about 20 seconds in and transforms into a giant soap cloud.
  6. Stop the microwave if your soap stops growing prior to 2 minutes to prevent burning.
  7. Carefully take the plate and the expanded soap out of the microwave.
  8. Let the soap cool before touching it.

Isn’t it cool? The expanded Ivory soap bar now resembles a meringue and is rigid enough so that you can pick it up in one piece.


We did the experiment twice because the kids just loved watching the soap erupt into this puffy cloud. I have to admit that I was quite amazed myself and wished I had more bars to throw in the microwave.

We did notice that the entire Ivory soap bar didn’t puff up. This is because we had to stop the microwave as the soap cloud was getting so big that it was touching the sides of the microwave. 

I took out the part that did not expand and threw it on another plate. I popped the plate with the remaining soap back in the microwave and the soap continued to expand until the entire thing puffed up.

If you don’t want to clean dry soap off your microwave after, you want to stop the microwave when the soap reaches the edge of the plate. That said, we now have one clean microwave from all the scrubbing!

I also want to note if you crush the soap cloud, it will break into powder. My son kind of went nuts with it and dust flew up into his nose and eyes. That was not fun. Be careful that your little ones handle the soap cloud gently.

The Science Behind the Ivory Soap Cloud

If you are lucky enough to perform the optional step, you will find out that the Ivory soap bar floats in water while soap bars from other brands do not. 

The reason why the Ivory soap bar can float in water is that it is less dense than water. But then how come it has a similar size and shape as the other soap bars?

One hypothesis would be that the soap bar is hollow on the inside. However, if you break it an half, you won’t find any big holes in the middle. 

The answer is that the Ivory soap bar has air whipped into it during the manufacturing process. Therefore, the final product contains numerous tiny air bubbles. All the air bubbles work together to make the soap less dense than water, allowing the soap bar to float.

The same air bubbles are what make the Ivory soap bar expand in the microwave. Similar to what happens when you heat up popcorn kernels, the air bubbles contain tiny droplets of water. When you heat the soap, the water vaporizes and causes the trapped air to expand. 

At the same time, the heat from the microwave causes the soap itself to soften, allowing the expanding gas to push the soap outward. 

What to Do with the Ivory Soap Powder After?

It’s just a waste to just throw away the soap cloud. But what can you do with the soap dust? 

We made our own soap bars out of them! Talk about the circle of life of an Ivory soap bar.

To reconstruct the Ivory soap bar, simply add some warm water to the powder and mix. I threw everything in the food processor and let the machine do the work. It reminds me of baking, but with a much more fragrant flour!

Take out the “dough” and put the mixture in a bowl. Let your kids pick out cookie cutters and fill them with your soap dough. Show your kids how to press down on the soap so that you don’t end up with a lot of air bubbles in the soap.

Ivory Soap Science Experiment Make Soap

Leave the soap dough in the cookie cutters for a couple of days in a dry area. Then after they dry, simply take them out and use them in the shower!


Final Thoughts on the Ivory Soap Science Experiment

The Ivory soap experiment is shockingly not the easiest experiment to clean up after. When we played with the soap dough, a lot of it got stuck on the dining table. Some pieces of the dough fell on the ground and got stepped on. Thank goodness my son loved using a sponge to wipe all the soap off because that took a long time.

That said, you do get a super clean table and floor afterward!


Ivory soap microwave science experiment pin

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