This invention relates to a system and process for modifying the resulting properties of a flash spun plexifilamentary film-fibril web and spunbonded nonwoven sheets made from such webs. In particular, the system includes specifically designed letdown chamber arrangements wherein the solution of polymer...http://www.google.com.au/patents/US5833900?utm_source=gb-gplus-sharePatent US5833900 - Process for modifying porosity in sheet made from flash spinning olefin polymer 
