Abstract: Improvements in the construction of postformable laminates are disclosed by the provision of a single high basis weight, high coarseness, high kappa number sheet formed predominantly of softwood pulp, preferably southern loblolly pine, which pulp has been treated in a mechanical device that effectively imparts kinking and curling to the individual pulp fibers. The sheet is intended as a replacement for the highly extensible sheet(s) currently located on the back of the laminate farthest away from the core.

Abstract: A water resistant corrugated paperboard material is prepared wherein the paperboard components (medium and liner or liners) are each coated on both sides with a thermoplastic film which acts as a water barrier and a water resistant adhesive for bonding the components together. The corrugated medium is also pretreated with an internal size treatment to prevent edge wicking, and, for the purpose of corrugating the medium without deleteriously affecting the thermoplastic film, the corrugating rolls are preheated to a temperature slightly less than the melting point of the thermoplastic film while a lubricating material is simultaneously applied to either the corrugating rolls or the medium at the corrugating nip.