This document describes methods of test using biaxial stress states for the determination of the tensile stiffness properties of biaxially oriented coated fabrics (properties along anisotropic directions, such as the weft and warp yarns for woven based coated fabrics, or along the courses and wales of knitted based coated fabrics). Other mechanical properties (such as pattern compensation values, shear stiffness, and strength) will be described in other parts.