Abstract: A thermally expandable multilayer packing for building material, having protruding parts and a body portion in the cross-sectional shape based a plane perpendicular to the longitudinal direction. The thermally expandable multilayer packing includes both a thermally expandable resin composition layer and a thermoplastic resin composition layer, wherein the thermally expandable resin composition forming the thermally expandable resin composition layer contains 100 parts by weight of a resin component containing a chlorinated polyvinyl chloride resin and/or an EPDM, 3 to 300 parts by weight of a thermally expandable graphite, 3 to 200 parts by weight of an inorganic filler and 20 to 200 parts by weight of a plasticizer. The thermally expandable resin composition layer and the thermoplastic resin composition layer are formed by simultaneous co-extrusion using the thermally expandable resin composition and the thermoplastic resin composition.