Abstract: A method of treating a membrane (16) comprises the steps of providing a membrane (16) with a structure of node (22) and fibrils (24). Surfaces of the nodes (22) and fibrils (24) define a plurality of pores (26) extending through the membrane (16). The membrane (16) is made from an expanded polytetrafluoroethylene material. A water-based dispersion of oleophobic fluoropolymer solids in a water-soluble solvent is provided. The dispersion has surface tension and relative contact angle properties such that the diluted dispersion is incapable of wetting the polytetrafluoroethylene material of the membrane (16). The dispersion is diluted with a liquid wetting agent so the diluted dispersion can wet the membrane (16). Surfaces of the nodes (22) and fibrils (24) are coated with the solids in the diluted dispersion. The wetting agent material and other fugitive material are removed.

Abstract: A composite membrane (12) comprising a membrane (16) with a structure of nodes (22) connected by fibrils (24). Surfaces of the nodes (22) and fibrils (24) define a plurality of interconnecting pores (26) that extend through the membrane (16) and between major sides (18, 20) of the membrane. The membrane (16) is made from an expanded polytetrafluoroethylene material which tends to tends to absorb oils and certain contaminating agents. The membrane (16) is moisture vapor transmissive, gas permeable and wind and liquid penetration resistant. A coating (28) is disposed on surfaces of the membrane (16) that define the pores (26). The coating (28) is made from an acrylic-based polymer with fluorocarbon side chains. The coating (28) is coalesced on surfaces of the nodes (22) and fibrils (24) to provide oil and certain contaminating agent resistance to the composite membrane (12) without completely blocking the pores (26) in the membrane (16).