Foam core foam plastic car. Foam core is mostly made of foam. Most commonly used are polyurethane foam, polystyrene foam and phenolic foam. The most commonly used load-bearing sandwich structural parts are rigid polyurethane foam and a newly developed foam core called combined foam. Beads, hollow ceramic microbeads or hollow plastic microbeads are a foam structure formed by adding ingredients, stirring evenly, and then solidifying with the help of a curing agent. This foam core is a good match for composite panels.