Plastic foams are lightweight, easily cut, excellent insulators, and good barriers to air and moisture. They are also strong enough to hold concrete and serve as the backer for interior and exterior finishes. The process fills them with countless tiny bubbles, much like a sponge.
Manufacturers create many different foams by varying ingredients and manufacturing methods.
It is the same as the white foam in many disposable coffee cups. XPS begins as a continuous mass of molten material. It is familiar as the yellow foam used in trays for fresh cuts of meat at the supermarket. Cement-foam composites are not actually a pure foam, but a mixture of Portland cement and loose EPS beads. Most ICF manufacturers mold their form units out of the foam they judge best for the job.