Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS), commonly called "Blue Board"
STYROFOAM Brand Insulation extruded polystyrene foam (XPS), owned and manufactured by Dow.
In this photo, EPS is pictured. Thermocol slabs made of expanded polystyrene (EPS) beads. The one on the left is from a packing box. The one on the right is used for crafts. It has a corky, papery texture and is used for stage decoration, exhibition models, and sometimes as a cheap alternative to Shola (Aeschynomene aspera) stems for artwork.
Section of a block of thermocol under a light microscope (bright-field, objective = 10×, eye piece = 15×). The larger spheres are expanded polystyrene beads which were compressed and fused together. The bright, star-shaped hole at the center of the image is an air-gap between the beads where the bead margins have not completely fused. Each bead is made of thin-walled, air-filled bubbles of polystyrene.