Over time, styrofoam has come to denote anything made from the rigid, foamy, typically white material that reveals tightly conjoined beads when snapped. Most people are not aware that the foam cups they use at the office drinking station and those little marshmallow-like chunks used for packaging are made from an entirely different material called Expanded Polystyrene (EPS).
While it is also a form of foamed polystyrene, EPS is manufactured by expanding polystyrene beads with steam and pressure then bonded together to form blocks and other shapes. The material is most commonly processed into coolers, wine shippers, molded end caps and corners and, yes, disposable cups and box packaging marshmallows.
Styrofoam, on the other hand, is a registered trademark of the Dow Chemical Company and its affiliates. It is made from extruded polystyrene and is largely moisture-resistant because of its closed cell structure. Because of this feature, the trademark material is primarily molded into panels called blue boards and used in construction for the insulation of walls and floors, and roof insulation systems. It is also often used in the floral, craft and special events industries.
Several companies offer a full range of polystyrene foam products, molding the sturdy material into balls, sheets, blocks, spheres, and cones that can be used for craftwork, special events, and other industries. If the project requires the material to have specific R-values and where compression strength is critical, it is better to make use of Styrofoam rather than EPS. Large-scale construction applications are a good example.