US Patent 7838123 Variable vapor barrier for moisture control in buildings

Disclosed is a variable vapor barrier for moisture control of buildings comprising or formed from a material having a moisture permeance of less than 0.1 perms (grains/h·ft2·inches of Hg) at less than 50% average humidity, such as from 10 to 50% or 20 to 40%; and a moisture permeance greater than 4, or greater than 10 perms at greater than 60% average humidity, such as from 60 to 90%, or 70 to 80%. Also disclosed are articles comprising the variable vapor barrier and methods of their use.