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Vapor Barrier

Vapor barrier is an impermeable membrane that blocks the flow of air through the building envelope.  A vapor barrier is an essential part of the building envelope.

Vapor Barriers vs Air Barriers

Confusion on the issue of vapor barriers and air barriers is common. The confusion arises because air often holds a great deal of moisture in the vapor form. When this air moves from location to location due to an air pressure differences, the vapor moves with it.

Building Construction - Moisture/Vapor Barrier

Vapor retardant slow the rate of vapor diffusion into the thermal envelope of a structure. Other wetting mechanisms, such as wind-borne rain, capillary wicking of ground moisture, air transport (infiltration), are equally important.

Moisture Penetration & UV Light Transmittance