Abstract: A method for making a paper sheet comprising at least one region which is thinner than the rest of the sheet. According to the method, a first paper layer (3) is formed on a wire in a first wet end of a paper-making machine, a second paper layer (5) is formed on a wire in a second wet end of the paper-making machine, one of the two paper layers has a number of localized tinner regions (8) so that the thickness (e2) of said paper layers in said regions is up to 50% less than the thickness (et) of the rest of the sheet, and the two layers are joined together and dried. The resulting paper may be used in banknotes or checks.

Abstract: The invention concerns an imprintable, flexible, synthetic support bearing at least one authentication or security mark.This support comprises:a substrate of synthetic materialat least one mark on at least one face of the support and consisting of at least one layer of a composition altering the substrate opacity,at least one layer of an imprintable pigment composition deposited on the face bearing the mark and optionally also on the substrate face without the mark, the mark being barely or not at all visible in reflected light and perfectly visible in transmitted light.Application to the security of synthetic paper.