The invention is an extrusion die (1; 1') comprising a tubular duct (2; 2') that extends between an inlet mouth (3) and an outlet mouth (4; 4') along an extrusion trajectory (X) with successive cross sections having progressively increasing widths and progressively decreasing heights. The extrusion trajectory (X) has a localized deviation (5) at the level of an intermediate cross section (6) of the tubular duct (2; 2').