US Patent 7521010 Fluoropolymer barrier material

A novel densified fluoropolymer article is described which has a water vapor permeation of about 0.015 g-mm/m2/day or less, and preferably has a matrix tensile strength of at least 10,000 psi in two orthogonal directions. The articles are made by compressing expanded porous PTFE at pressures, temperatures and times which result in elimination of the pores, and subsequent stretching above the crystalline melt temperature.