Abstract: A shape molding operation is performed to form a three dimensional building panel. The operation involves providing a mold having a cavity, the cavity having dimensions essentially identical to a finished three dimensional building panel suitable for installation. The shape molding operation involves pre-heating at least one of two major internal surfaces of the mold; introducing polystyrene foam beads into the cavity; heating the polystyrene foam beads; and causing the heated polystyrene foam beads to flatten and spread against the pre-heated major internal surface of the mold, thereby forming a sealed water-repellant skin at least on a face of the three dimensional building panel. In view of the corresponding size of the mold cavity, no cutting action is required on the expanded polystyrene (EPS) foam formed therein, so that a least a building-contacting face of the resultant boards acquires the sealed water-repellant skin that is otherwise lost when forming boards from buns of the prior art.