Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS) . It is a lightweight and buoyant material composed of 98% air, making it ideal for use in insulation, packaging, and as a water barrier. Styrofoam is manufactured to provide continuous building insulation board used in walls, roofs, and foundations as thermal insulation. The claimed R-value of Styrofoam insulation is five per inch. The term Styrofoam is often used in the United States as a colloquial term to refer to expanded (not extruded) polystyrene foam (EPS) . EPS is most commonly referred to as simply "polystyrene" outside the United States. Polystyrene (EPS) is often used in food containers, coffee cups, and as cushioning material in packaging. EPS is made from polystyrene, a plastic that’s often used to make clear products like food packaging or lab equipment. When polystyrene is combined with colorants, additives, or other plastics, it can be utilized in the creation of toys, car parts, appliances, and much more.

In summary, Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam used primarily for insulation, packaging, and as a water barrier. It is often confused with expanded polystyrene foam (EPS), which is used in food containers, coffee cups, and as cushioning material in packaging.