Abstract: Composite panels are disclosed which comprise outer layers derived from cellulosic and like material conventionally employed in particle boards and an inner layer which is comminuted scrap plastic material, the various layers and the particles in them being bonded together using an organic polyisocyanate binder. Optionally the binder contains an internal release agent. The composites, in addition to representing a valuable way in which to utilize scrap plastic, also possess improved properties compared with the corresponding panels which lack the inner core. In a particular embodiment the scrap plastic used is derived from junked automobiles.