The results of this test method will indicate the relative permeability by water vapor of the tape through its smallest dimension (generally normal to the tape's backing).

The pathway for the water vapor parallel to the adhesive-cup interface is great compared to the tape's thickness and the latter is usually the nearly exclusive source of transmitted vapor.

Some tape types allow a relatively free path in a direction normal to the backing or along backing pathways parallel to the adhesive-cup interface allowing the adhesive to become the principal barrier.

If the adhesive does not continue to adhere to the cup flange during the exposure periods allowing unintended pathways for water vapor to occur, the measurement should be considered as not having been made. Consequently, the tape might be considered as being inappropriate for use on surfaces like the cup flange under moisture conditions approximating those of the test.

Note 1—It may be that the interest is simply in the tape material as a water vapor barrier. In this case, how well the tape adheres to the cup flange may be of little consequence, and steps to prevent any edge effects are in order. These are referred to in Section 10.

1.1 This test method covers one procedure for measuring the water vapor transmission rate of pressure-sensitive tape.

1.2 The values stated in either SI or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system must be used independently, without combining values in any way.

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.