disclosed is a method for producing a three - dimensional composite structure and a method for producing the mold for the three - dimensional composite structure . the mold is formed of at least one rigid die member and a second thermoplastic die member . the second thermoplastic die member is formed by coupling a rubber flexible pattern to a surface of the first die member . vacuum or pressure is applied to a heated thermoplastic sheet to cause the heated thermoplastic sheet to deform about the flexible pattern , thereby forming the second die . strips of reinforced polymer thermoset pre - preg material are then positioned within the cavities formed by the flexible pattern and are allowed to cure . optionally , heat , pressure , and vacuum may be applied to the mold construction to facilitate the curing of the thermoset materials .