Method of making syntactic foam core material

A syntactic structural foam product in flat sheet form or curved three-dimensional form adaptable to such uses as a light weight structural core for composite laminates, is made of a mixture of hollow ceramic microspheres and dry resin powder, of either thermosetting or a high-temperature thermoplastic resin, distributed in the interstices of the mass of microspheres for integration of the mixture into desired form upon heating and cooling. Resin powder collected as a waste by-product from resin coating materials can be recycled in the production of the desired product. The foam product is produced by first intermixing the microspheres and powdered resin by physical agitation of the mixture and depositing the mixture as a layer over a surface having a release agent thereover within a dimension defining region between boundary members and then supplying heat with or without pressure to the layer at a temperature and for a time period sufficient to effect a melting of the resin powder and thereafter cooling the resin in a hardened condition to integrate the mixture into the product desired after which the product is withdrawn from the forming zone. Reinforcing elements such as glass or carbon fibers can be selectively included in the mixture for predeterminable desired physical and mechanical properties.