Abstract A STRUCTURAL MATERIAL HAVING EXCELLENT ACOUSTIC TRANSMISSION PROPERTIES COMPRISES A PARTIALLY ELASTOMERIC, LOW DENSITY PANEL OF COMPOSITE CONSTRUCTION. IN ONE EXAMPLE A NUMBER OF LAYERS OF A LIGHTWEIGHT SYNTHETIC FABRIC DEFINE A TRANSMISSION PANEL OF APPRECIABLE THICKNESS AND INCLUDE APPROXIMATELY 50% BY WEIGHT OF A RESIN MATRIX MIXTURE WHICH IS OF APPROXIMATELY 50% ELASTOMERIC MATERIAL. PREFERABLY ALSO, THE MATRIX MATERIAL INCORPORATES APPROXIMATELY 10% BY WEIGHT OF THIN WALL GLASS MICROSPHERES. FURTHER INCREASES IN STRUCTURAL PROPERTIES MAY BE OBTAINED, WITHOUT UNDUE SACRIFICE OF TRANSMISSION PROPERTIES, BY INCORPORATING THIN INNER AND OUTER SHELLS JOINED TO THE MULTI-LAYER COMPOSITE CORE.