**Custom Sizes Available** What is Expanded Polystyrene (EPS) foam? The word Styrofoam™ is often used to describe expanded polystyrene (EPS) foam; however, ‘Styrofoam’ is actually a trademarked term for closed-cell extruded polystyrene foam made for thermal insulation and craft applications. EPS foam is the correct term for any form of expanded polystyrene. Expanded Polystyrene insulation is a lightweight, rigid, closed cell insulation. EPS is available in several compressive strengths to withstand load and back-fill forces. This closed-cell structure provides minimal water absorption and low vapor permanence.