Abstract: This invention relates to a preparation process of a biaxially oriented heat-shrinkable ultra-thin film, biaxially oriented by the flat process and made of linear low-density polyethylene, characterized in that:an ethylene homopolymer or an ethylene and C.sub.4 to C.sub.18 alpha-olefinic comonomer copolymer of a density lying between 0.89 and 0.94, alone or in combination, are heated beyond the melt temperature and extruded,the extruded film is poured and cooled at the appropriate hardening temperature,the film is drawn a first time in the machine direction at the appropriate temperature between 3 and 7 times the initial dimension of the non stretched film,the film is drawn a second time in the transverse direction at the appropriate temperature between 3 and 15 times the initial dimension of the non stretched film, the biaxially oriented film is drawn a third time in the machine direction at the appropriate temperature between 1.

Abstract: A method of preparing paper for filter bags, the method of the type comprising a step during which a non-woven paper is prepared comprising two superposed layers, namely a layer based on synthetic fibers and a layer of cellulose fibers, by a technique which is known per se, wherein the method includes a subsequent step of subjecting the non-woven paper to a calendering operation between a support structure and a heated cylinder having projections. The present invention also provides apparatus for implementing the method and products obtained in this manner.