a method of manufacturing a composite sandwich structure , the method comprising a preform assembly method . the method comprises providing a preform comprising at least two sheets connected by a plurality of extensible threads , and affixing to the outer face of each sheet , a face sheet . the adhesion is by a film adhesive placed over the respective sheets , and the preform is subjected to pressure or heat to set the film adhesive . the method further comprises a method of molding a composite sandwich structure , the method comprising placing a preform in a mold , creating pressure differentials between respective chambers within the mold , feeding a resinous compound into the mold , and allowing the resinous compound to set and cure . the invention also provides composite sandwich structures made in accordance with the methods .