Erupting Foam

Just mix the two liquids together and watch closely!

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Just mix the two liquids together and watch closely as the foamexpands to 30 times its original size! Don’t be fooled by thelooks of the foam – it actually turns into a solid material calledpolystyrene.

Here's What You'll Need

  • Polyurethane Foam System (Part A and Part B) - Available from Flinn Scientific at (800) 452-1261 or from your local plastic materials company
  • A disposable spoon
  • Disposable cups (clear plastic, if available)
  • Food coloring (optional)
  • Wax paper
  • Safety glasses
  • Plastic gloves


  1. Put on your safety glasses and gloves.
  2. Measure 2 ounces of Solution A into a disposable cup and 2 ounces of Solution B into a second disposable cup. Note: The volume of A and B should be approximately the same.
  3. Add a few drops of food coloring to either liquid to jazz it up.
  4. Spread wax paper (or a large plastic bag) on the table and place one of the plastic cups in the center of the wax paper.
  5. Pour the liquid from the second cup into the cup on the wax paper and stir the liquids thoroughly. Be careful not to drip any of the liquid onto the floor, table, clothes, or anything else of value. Keep mixing until you start to see the foam beginning to expand.
  6. The foam will expand to 30 times its original volume. The cups will actually get warm – this indicates an exothermic reaction.

How Does It Work?

There are many forms of polyurethane such as fibers, coatings, elastomers, flexible foams, and rigid foams. The foam in this system is a rigid foam that is used in furniture, packaging, insulation, flotation devices, and many other items. Here, a rigid polyurethane foam is produced by mixing equal parts of two liquids, called Part A and Part B. This lightweight foam expands to about thirty times its original liquid volume and will become rigid in about five minutes.

Additional Info

Reference: Additional information on this reaction is available through Flinn Scientific at (800) 452-1261.

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