Perm Inch
Perm Inch :
A traditional unit of water vapor permeance. The perm value (see above) does not depend on the thickness of the material used as a water barrier. The permeance is the product of the perm value and the thickness, measured ininches. One perm inch equals about 1.453 x 10-12 kg/(m·Pa·s) at 0 °C or about 1.459 x 10-12 kg/(m·Pa·s) at room temperature. The SI unit kg/(m·Pa·s) actually simplifies to seconds (s)
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