Abstract: The invention relates to a biaxially orientated, single or multi-layered porous film made of propylene homopolymer and/or propylene blockcopolymer and ss-nucleation agent. Said film has a Gurley value of between 50 to <400 s and shrinkage in the longitudinal direction of <5% at 100 DEG C./1 hour, and a transverse shrinkage of <10% at 100 DEG C./1 hour.

Abstract: The invention relates to a method for raising the surface tension of biaxially-stretched films made of thermoplastic polymers. According to the method, a film is first treated on a surface by means of an atmospheric pressure plasma before being stretched transversally or simultaneously across the width thereof, and the film is additional a subjected to a second treatment by means of a corona or flame after being stretched transversally or simultaneously, the second treatment being done on the same surface which has already been plasma-treated.