Abstract: A plastic sheet material comprising a pair of opposed faces between which run a series of elongate voids, the voids being arranged such that there are a series of uninterrupted interconnections between the two opposite faces. The voids are of a cross-sectional shape such that there is a substantial absence of sharp corners. Where the voids are not in themselves round, the corners are radiussed. In a preferred construction, two series of interconnections are provided which join one another where they meet. The construction is particularly useful in packaging, especially the packaging of food products. The present invention has high buckling resistance in both the machine and cross-machine directions and is particularly resistant to torsional stresses, compression and/or extension and demonstrates good impact resistance.