An assembly useful for providing structural reinforcement and/or sound/vibration damping to a hollow member of a motor vehicle is provided which contains an injection-molded carrier made of a heat resistant thermoplastic composition, at least one of the first side and the second side of the carrier has at least one receptacle adapted to receive and retain an insert comprised of a heat-expandable resin composition. The carrier may have a plurality of openings in at least one of the first side or the second side forming a grid or lattice and the assembly may include a mounting member adapted to fasten the carrier to an interior wall of a hollow member.