Abstract: An improved molding apparatus for expanding beads of polystyrene material into large blocks in the manufacture of insulating material. The mold apparatus has walls made from a plurality of tubular wall members arranged in horizontal, side-by-side relation. The wall members are mounted transversally within encircling frames. Steam is supplied to each wall member, and from within each wall member, into the mold cavity to expand the polystyrene beads held therein into a block. An improved device is also provided to remove the block from the mold cavity.