A process for manufacturing a sheet material comprising at least two fibrous plies juxtaposed one on top of the other, including the following steps: a first paper ply is produced by filtration of an aqueous suspension of fibers on the wire cloth of a cylinder mold or of a former; a second paper ply is produced on the wire cloth of a second cylinder mold so as to form at least one recess in the second ply; at least one at least partially transparent element is placed between the two plies that are still wet; and the two plies are joined together so that said at least one recess of the second ply, the at least one at least partially transparent element and the at least one elongate region of zero thickness of the first ply are situated facing one another; then drying the obtained structure.