Ivory Soap Explosion

Learning Objectives

Heat energy plays a critical role in natural processes and in human life. Students will investigate the effect of heat on a solid object, and observe the effect on its volume.

Associated Curriculum Topic

Heat in the Environment


  • Bar of Ivory Soap (must be Ivory brand, other brands will not work)
  • Microwave
  • Plate (microwave safe)


In the manufacturing of bars of Ivory soap, the ingredients are whipped together. In the whipping process small air bubbles get trapped in the bar of soap. The air bubbles are so small that the naked human eye cannot see them. The air pockets allow for some interesting properties of Ivory soap. One of the main properties that students may know about is that Ivory soap floats when placed in water. However, the students may not know what happens to it when it is placed into a microwave oven. A microwave oven generates electromagnetic waves in the microwave region, which are a form of energy that is transferred to object in the oven. When the Ivory soap is place in the oven, the air molecules inside the pockets obtain more energy, which cause them to move more quickly. A molecule that has a higher amount of energy requires more space to move around in and therefore the soap grows in size inside the microwave.


  • cut bar of soap in half (a full bar will make a big mess in the microwave!)
  • place piece soap onto the microwave safe plate
  • microwave the soap for no more than 30 seconds on high

Below are before and after photos of a small piece of ivory soap placed in the microwave.

Cube of Ivory soap on a plate Expanded Ivory soap on a plate after going in the microwave
Before After

Investigating Questions

  • How is the soap different before and after it is heated in the microwave?
  • Why does this happen?
  • Do you think any type of soap would work?