Patent ID: 8840824

Claim:
A method of processing PTFE, comprising: extruding a compounded PTFE resin through an extruder in a machine direction to form a PTFE ribbon extrudate; calendering the PTFE ribbon extrudate in the machine direction to form a planar layer of PTFE having an upper surface and a longitudinal length in a machine direction of an extruder used to produce the layer of PTFE and having a width in a cross machine or transverse direction; selectively applying an isoparaffinic stretching agent to the layer of PTFE in a predetermined pattern comprising a plurality of first lateral zones within the layer of PTFE being substantially saturated with the applied isoparaffinic stretching agent and a plurality of second lateral zones within the layer of PTFE with substantially none of the applied isoparaffinic stretching agent; providing a tentering machine; and stretching the layer of PTFE in the tentering machine in the transverse direction to the machine direction while the plurality of the first lateral zones of the layer of PTFE are fully saturated with the stretching agent throughout their thicknesses during stretching; wherein the plurality of the first lateral zones have a shape selected from the group consisting of squares, rectangles, circles and ellipses; wherein, after stretching, the plurality of the first lateral zones of the PTFE layer have substantially no fluid permeability with a Gurley Number of greater than 12 hours for 100 cc of air at a pressure of 12.4 cm of water; and wherein, after stretching, the plurality of the second lateral zones of the PTFE layer have substantial fluid permeability with a Gurley Number of less than about 15 seconds for 100 cc of air at a pressure of 12.4 cm of water.