Abstract: Shaped, foam plastic parts are made in a lightweight shaped, open trough-like mold having a coherent sheet metal interior comovable insert and related comovable floating lid, wherein said insert is positioned and adapted to slidably elevate within the interior surface of said trough coincident with the expansion of an internally housed and expandable foamable reaction mixture. As the reaction mixture expands, the foam freely expands upwardly during a first stage of the method to at least a height of approximately 50% of that desired for the plastic part. At that point the expanding foam engages an inwardly projecting flange portion of the comovable insert upon which is seated a comovable floating lid.