A synthetic board is made from a plastic film ply 4, 6 adhered or welded to a parallel array of thin-walled plastic tubes 2. In some versions, the tubes are spaced from each other. In others the tubes are contiguous. This allows the board to curl up more or less depending on the tube packing about the tubes axes but to resist bowing between the ends of the tubes. The board is useful for packaging, display, cladding and insulation. In some versions, a second parallel array 7 lies at 90° to the first and the board is free to fold about the boundary between the two arrays. In this way, runs of cruciform carton blanks can be manufactured. The tubes can contain particulate or gel filling.