But it is made of wood fibers that are glued together. Polyisocyanurate foam is also known as Iso board. It usually has an asphalt felt or a fiberglass facer on both sides. There are two types of rigid polystyrene insulation boards. Expanded polystyrene is usually called EPS or bead board.
Extruded polystyrene looks somewhat like expanded polystyrene.
But it has a smooth, skin-like surface. There usually is a facer on one or both sides. A rigid insulation layer can be laminated to OSB or plywood. This is an insulated deck that is nailable. Other composite boards are coated with asphalt or some other facer materials.