Purchase rubber foaming agent from a chemical supplier. Compare prices online to find the lowest-cost material; consider buying in bulk for additional savings. Foaming agent is also referred to as blowing agent.
Purchase emulsion-grade polymer vinyl chloride paste resin. This material is often available from international suppliers that can be located on the Internet, but it must meet the American Society for Testing and Materials standards for classroom use. An extensive list of current suppliers can be found at sites such as Alibaba.com, which specializes in global trading.
Combine the appropriate amount of foam agent and vinyl chloride according to package directions. Follow all foam agent package instructions carefully and precisely.
Pour the liquid mixture into the foam mold. Any metal item, such as a bowl or cake pan, can be used as a mold to shape the polymer foam as desired.
Allow to set for the amount of time recommended by the foaming agent instructions before removing the mixture from the mold.