Which Side of the Insulation Is the Vapor-Retardant Side?

Vapor Barrier Facings

• There are two types of material that are most commonly used as vapor barrier facings on batt insulation -- kraft paper and aluminium foil. Both are affixed to the batt with an asphalt-based glue that further prevents the passage of moisture.

Which Side?

• Faced insulation batts come with one side covered with the facing. The smooth feel of the foil or paper contrasts with the rougher, more uneven texture of the unfaced side. But loose fibers can irritate the skin, so do not touch the unfaced side without protective gloves. When installing the insulation, the faced side should be turned so that it faces the interior of the room.

Why Have Facing?

• Vapor barriers are fixed to insulation batts primarily to prevent moisture from seeping into the fiberglass or wool. In areas such as attics and basements, condensation can form. If condensation seeps into the insulation, it compresses the material, reducing its effectiveness as an insulator, and this can result in mold or mildew forming. Facings on insulation batts can also serve as barriers to prevent insects from burrowing into the insulation, which would allow air and moisture to penetrate, impacting the insulation's effectiveness.

Caution

• Remember that both kraft paper and foil facings are combustible, meaning that they will ignite if exposed to high enough temperatures. Do not leave faced insulation exposed to the room. Cover it with drywall or a similar fire-resistant material. Also, do not place faced batt insulation around furnace ducts, flues or other types of heating pipes.