Process for manufacturing a sheet material

A method for manufacturing a sheet material including at least two fibrous plies juxtaposed on each other, said method including the following steps:

• making a first paper ply, including at least one elongate area of zero thickness, by filtration of an aqueous suspension of fibers on the wire of a first round mould or of a former,
• making a second paper ply on the wire of a second round mould in order to form at least one recess in the second ply,
• positioning at least one at least partly transparent element between two plies still moist and joining both plies so that said at least one recess of the second ply, said at least one at least partly transparent element and said at least one zero thickness elongate area of the first ply are located facing each other,
• drying the thereby obtained structure,
• said at least one at least partly transparent element being a continuous strip and having the same length as said at least one zero thickness elongate area of the first ply.

A sheet material including:

• at least two fibrous plies juxtaposed on each other,
• a first paper ply, including at least one elongate area of zero thickness,
• a second paper ply,
• at least one recess in the second ply,
• at least one at least partly transparent element between both plies, said at least one recess of the second ply, said at least one at least partly transparent element and said at least one zero thickness elongate area of the first ply being located facing each other,
• said at least one at least partly transparent element being a continuous strip and having the same length as said at least one zero thickness elongate area of the first ply.