Particleboard is perhaps the least expensive core for hardwood plywood because its particles are less refined than MDF, yet it is perfect for many applications. It is smoother and more uniform than veneer cores and available in Class A fire ratings as well as no-added-urea-formaldehyde constructions. Particleboard is generally available 1/2" or thicker. While some hardwood plywood producers manufacture their own particleboard, most outsource this core material.