Abstract: Pre-expanded styrene polymer particles, which may contain one or more pre-expanded styrene polymer beads, are coated with sufficient water glass so that the particles, when dried to a reversible, tack-free pourable state, comprise from about 30% to 80% styrene polymer solids. The particles may be shaped into a desired article configuration and then dried to a tack-free state, the particles adhering together through the water glass, and the resulting article having a bulk density of from about 1.25 lbs. to 3 lbs. per cubic foot. The water glass or the pourable particles may be treated to decrease alkalinity and to cause irreversible precipitation of water glass solids, rendering the final product essentially waterproof.