Disclosed is an expanded organic foam material having excellent thermal resistance and durability. The expanded plastic foam material is produced by preparing plastic beads or plastic foams, modifying silicate with at least one selected from among an alkaline earth metal compound, an alkaline earth metal compound-containing material, and an acid, coating the modified silicate on the prepared plastic beads or plastic foams, melt-molding the coated plastic beads or plastic foams while applying heat and pressure thereto, and drying the molded material. Also, the expanded organic plastic foam material has good impact-absorbing properties, easy formability, excellent sound-insulating and sound-absorbing performance and thermal insulating performance, good flame retardancy and thermal resistance, and improved water resistance and durability.