Term Description
Vapor retarder

A material or system that significantly impedes the transmission of water vapor under specified conditions.
Vapor retarder class

A measure of a material or assembly’s ability to limit the amount of moisture that passes through that material or assembly. Vapor retarder class shall be defined using the desiccant method of ASTM E96 as follows:

Class I: 0.1 perm or less.

Class II: 0.1 < perm ≤ 1.0 perm.

Class III: 1.0 < perm ≤ 10 perm.
Water vapor retarder

See ‚"vapor retarder.‚"