Using perms to measure the amount of water vapor able to pass through a material. Perm = one grain of water vapor per square foot, per hour, per inch of mercury pressure differential (0.491 psid).

A sheet of paper's rate of water vapor penetration.

The rate of movement of moisture vapor in unit time through a unit area of a membrane.

The rate at which water vapor permeates through a plastic at a specified temperature and relative humidity.

The rate water vapor permeates a plastic wall at specific temperatures and relative humidity.

A measure of the rate of water vapor transmission through a P.S. label.

The process by which moisture moves through a slab of concrete. This is impacted by temperature, humidity and vapor pressure.