Abstract: Process designed to obtain a sheet of thermoplastic material containing at least on one side a decoration consisting of parallel stripes of different colors juxtaposed to each other and capable of being thermoformed to produce hollow volumes containing the same initial decoration, characterized in that it consists in extruding simultaneously, through a single multiple duct die, firstly a monochrome basic layer, secondly at least one intermediate decoration layer, formed of longitudinal, juxtaposed stripes of different colors, and lastly at least one upper transparent layer overlapping said intermediate layer, all said layers being combined in a die area as close as possible to its outlet.