A winding or storage reel for large, continuous lengths of flexible materials such as cable, rope or paper is collapsible into substantially flat components for recycling transport. The reel core is preferably twin sheet, vacuum formed of thermoplastic sheet material and comprises a plurality of laterally hinged stave elements in substantially circular alignment between a pair of end flanges. Threaded assembly rods compress the core stave elements between the end flanges. The adjacent lateral edges of the several stave elements are parallel to the core axis and are flexibly joined to hinge about an axis parallel to the lateral edge. One pair of laterally adjacent edges in the core circle are non-pivotally joined by respectively meshing fingers. Two integral plastic sheets respective to inside and outside shell walls are thermoformed to integrate all or several stave elements and hinges into a continuously single component that can be manually formed into the closed perimeter of the reel core cylinder for support of an over-wrapped material. For return transport, the closed perimeter of the core component is opened along the joint edge and developed to a substantially flat configuration.