In electrodes and biosensors poly(vinyl chloride) (PVC) membranes were plasticized to 200 parts per hundred resin, independent of plasticizer specie. Puncture tests quantified five mechanical properties for at least eight levels of seven plasticizers. Using Citroflex B-6 at a phr ratio of 0.31, the strength and secant stiffness peaked at 9.63 N and 1250 N m(-1), respectively. At a phr ratio of 0.6 the toughness peaked at 48 N mm. These three properties decreased at higher phr ratios for all plasticizers. Tangent stiffnesses were generally 1.7 times secant stiffnesses. For all plasticizers, ductility increased to a constant value of 15 mm at a phr ratio of two. The molecular structures of the plasticizers influenced the mechanical properties. For a given phr ratio, plasticizers having lower hydrodynamic volumes increased the strengths, stiffnesses, and toughnesses of the membranes. Compared to prior dielectric testing, the strength, toughness, and stiffness increased as the ionic resistivity increased. In electrodes and biosensors phr ratios should be reduced to a minimum of one.