An integrated reinforcing crossmember adapted for positioning within a cavity of a structural member, comprising: a carrier having a center section and two end sections (5,7), each end section (5,7) being joined to the center section, the center section of the carrier having at least two external lateral walls and at least two internal ribs running generally in the direction of the longitudinal axis of the crossmember, the external lateral walls and internal ribs intersected by a plurality of cross walls running cross-sectionally across the crossmember, each external lateral wall further joined to its most adjacent internal rib by a first horizontal connecting wall, and respective pairs of adjacent internal ribs further joined by a second horizontal connecting wall, and each end section (5,7) of the carrier having at least two external lateral walls and at least two internal ribs running generally in the direction of the longitudinal axis of the member, the external lateral walls and internal ribs joined by a plurality of cross walls running cross-sectionally across the crossmember, each external lateral wall further joined to its most adjacent internal rib by a third horizontal connecting wall, and respective pairs of internal ribs further joined by a fourth horizontal connecting wall, wherein each external lateral wall of each end section (5, 7) is comprised of an external lateral plane, an expansible material is disposed on at least a portion of each external lateral plane of each end section (5,7) and on at least an external portion of each third horizontal connecting wall, and the expansible material expands when activated to contact a surface within the cavity of a structural member, characterized therein that the external lateral walls of the center section are configured to be closer to the center longitudinal axis of the crossmember than the external lateral walls of each end section (5,7). a carrier having a center section and two end sections (5,7), each end section (5,7) being joined to the center section, the center section of the carrier having at least two external lateral walls and at least two internal ribs running generally in the direction of the longitudinal axis of the crossmember, the external lateral walls and internal ribs intersected by a plurality of cross walls running cross-sectionally across the crossmember, each external lateral wall further joined to its most adjacent internal rib by a first horizontal connecting wall, and respective pairs of adjacent internal ribs further joined by a second horizontal connecting wall, and each end section (5,7) of the carrier having at least two external lateral walls and at least two internal ribs running generally in the direction of the longitudinal axis of the member, the external lateral walls and internal ribs joined by a plurality of cross walls running cross-sectionally across the crossmember, each external lateral wall further joined to its most adjacent internal rib by a third horizontal connecting wall, and respective pairs of internal ribs further joined by a fourth horizontal connecting wall, wherein each external lateral wall of each end section (5, 7) is comprised of an external lateral plane, an expansible material is disposed on at least a portion of each external lateral plane of each end section (5,7) and on at least an external portion of each third horizontal connecting wall, and the expansible material expands when activated to contact a surface within the cavity of a structural member, characterized therein that the external lateral walls of the center section are configured to be closer to the center longitudinal axis of the crossmember than the external lateral walls of each end section (5,7).