Abstract: A multi-panel hollow door has a core made of corrugated paperboard. The core is formed from a stack of plies in which adjacent plies are adhered to one another in accordance with a predetermined pattern of adherence (e.g., a gluing pattern). The stack is expanded in a direction perpendicular to the plies to form an elongated series of cells disposed longitudinally between transversely spaced panel indentations of a door skin, at a central region of the door. Each cell has a pair of transversely spaced vertices, and juxtaposed end portions of vertex-forming plies form tabs. Each tab is preferably oriented to overlap an adjacent portion of a vertex-forming ply, the desired orientation being obtained by partial slitting of a single vertex-forming ply. Unexpanded end portions of a stack of plies may be broken off to form pads between corresponding portions of the skins.