1.1 This test method covers the determination of the resistance of nonporous paper to the passage of air. This test method cannot be used in those cases where the paper cannot be clamped securely against surface and edge leakage, such as, crepe or corrugated papers.

1.2 This test method is applicable to papers that permit the passage of up to 25 mL of air/0.785 in.² in 15 s, and in general, to papers not sufficiently porous to be tested by TAPPI methods T460 and T536.

Note 1 - For testing pourous and semiporous paper, refer to TAPPI T460, and T536, respectively. Since the three methods (D 726, T460, and T536) do not give the same results, it is recommended that a specific method be agreed upon in specifications covering paper between the seller and the purchaser, and that the method be chosen to conform to the principle range.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.