Low permeability and high strength woven fabric and methods of making the same

A method for producing a woven fabric, said method comprising:

• (a) weaving fibers in a warp direction and a weft direction to form a fabric having a top surface and a bottom surface, wherein the warp fibers and weft fibers each comprises one or more filaments of a synthetic polymer having substantially uniform cross-sectional composition;
• (b) calendering the fabric in the presence of heat and a heat transfer liquid or vapor added during the calendering step or added in a prior step of the fabric production process and retained by the fabric, wherein the calendering step permanently modifies the cross-section of at least a portion of the filaments in the fibers on the top surface of the fabric or at least a portion of the filaments in the fibers on the bottom surface of the fabric to produce a treated fabric having a tensile strength in both the warp and weft directions of 1000 N or greater and having, in the absence of any coating, a static air permeability (SAP) of 3 l/dm2/min or lower.

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A method for increasing the process speed at which hot roll calendering of a woven fabric is performed to attain a selected air permeability value, wherein the fabric has a tensile strength in the warp or weft direction of ≥1000N, said method comprising the step of hot roll calendering the fabric in the presence of an added heat transfer liquid or vapor, wherein at least one physical property of the fabric other than air permeability is improved as compared to that of the same fabric calendered in the absence of the added heat transfer liquid or vapor to attain the selected air permeability value.