This invention is directed to improvements in fibrous sheets, such as paper, incorporating an elongate impermeable element, to a method of making such paper and to documents made therefrom. The method comprises the steps of bringing an elongate flexible element into contact with a moving support surface, and depositing fibers onto the support surface to form a fibrous sheet which travels in a machine direction. The said support surface has spaced portions which prevent the substantial deposition of fibers at those portions and form windows at spaced locations in at least one surface of the sheet. The deposition of fibers is carried out in such a manner that as fibers are deposited onto the support surface the elongate element is incorporated in the sheet with regions of the element at least partially exposed at at least one surface of the sheet at said windows. At least a leading edge of the spaced portions is at an angle, in the plane of the sheet, which is not 90.degree. to the machine direction.