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cooling the resin in a hardened condition to integrate the mixture into the product desired after which the product is withdrawn from the forming zone .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 .