ceiling tile further it is believed that this carbon black acts as an inert filler or retardant agent which prevents the densely packing of the glass fibers on the interior surface by physical separation of fibers and resin and thereby provides the fibrous textured surface disclosed in fig5 other inert fillers could be used to achieve the same effect as can be seen from fig2 the intermediate layer 36 does not extend into the peripheral edge portion of the curvilinear wall 8 this insures adequate adhesion between the three fiberglass layers to provide a relatively dense twelve pounds per cubic feet edge portion to assist in both supporting the weight of the plenum chamber and to strengthen the mounting of the perforated faceplate 10 during manufacturing fiberglass layers 28 32 and 34 are cut to an appropriate identical size while fiberglass layer 30 and the intermediate layer 36 are cut to a smaller size and are concentrically mounted in the mold cavity between the top mold die set 38 and the lower die punch assembly 40 the mold walls can be formed of one fourth inch steel and are only shown schematically in fig2 and 3 a peripheral knife edge member 50 can cut any excessive fiberglass laminae extending beyond the mold cavity the top mold 38 and die punch assembly 40 includes manifolds 42 for receiving heated air to provide the curing temperature cooling means such as heat exchange water conduits not shown can also be utilized to maintain accurate alignment of the mold platens with a convention tie rod assembly not shown the tie rod assembly can be connected to either a mechanical or a hydraulical source of power for forcing the top and.