Low-elasticity spacer for hollow-core structures

An expandable， low-elasticity spacer made of two-sided corrugated material having a topsheet， a bottomsheet， and a corrugated sheet therebetween forming flutes. The spacer comprises two strips of the corrugated material， joined together to form a polygon having inside and outside corners. Each outside corner of the polygon has a slit parallel to the flutes that severs the continuity of the sheet in which it is made， eliminating the ability of the discontinuous portions to pull against each other， thereby eliminating potential spring back. The spacer is perforated， scored or crimped parallel to the flutes in one or more of the inside corners to make it easier to bend the spacer at the desired fold line. Because the spacer avoids springing back to its collapsed position， it can be sized to fill a cavity with no excess material and leave no unintended gaps. The corrugated material is preferably fiberboard or plastic.