Design Nomenclature / Physical Model Making
XPS foam
Also called blue foam, pink foam, extruded polystyrene, XPS, insulation foam, Styrofoam
Closed-cell extruded polystyrene board, sold as building insulation and used as the fastest massing material there is. It carves with a knife, sands to a true surface, and takes a hot wire. Solvent paints and CA glue dissolve it on contact — it needs a water-based or plaster barrier coat before anything else touches it.
In practice
"Styrofoam" is Dow's trademark for exactly this board. The white beaded cups are EPS, a different foam that crumbles instead of carving.