Styrofoam is a registered trademark for the Dow Chemical brand of extruded polystyrene foam (XPS). It is usually blue or pink in color and made in the form of a sheet.
Expanded polystyrene (EPS) is a bead type foam which can be molded into shapes, blocks, and sheets. It is typically white in color but can be died to any color. EPS is frequently but erroneously referred to a Styrofoam.