Composite membrane having oleophobic properties

An air permeable sheet material comprising:

• a polymeric porous base membrane comprising a plurality of nodes and fibrils defining a plurality of interconnecting pores extending therethrough, each said node and fibril comprising a surface;
• and
• a precipitated coating material deposited on substantially all said surfaces of said plurality of nodes and fibrils, said coating material comprising a copolymer formed from a fluorinated acrylate, butyl acrylate, and a monoisocyanate crosslinker having the following structure:
• said precipitated coating material applied from a low surface tension fluid capable of entering said pores in said porous base membrane, said coating material precipitated on said surfaces of said plurality of nodes and fibrils upon rendering said coating material insoluble in said low surface tension fluid;
• said precipitated coating material providing oil and contaminating agent resistance of at least a number six measured in accordance with AATCC 118 test method.