This standard is intended to describe procedures for determining the water vapor permeability of sheets of paper, transparent sheets, sheets of plastics, and other sheets of materials bonded with plastics. There can be considerable difference in the permeability of a plastic sheet when its two sides are exposed, respectively, to low humidity on one side and medium humidity on the other, and high humidity on one side and medium humidity on the other. These methods provide the procedures to measure permeability under these conditions.