Fiber Glass

Glass fibers do not absorb moisture, however, moisture can condense in air spaces within the insulation and migrate to parts of the insulated assembly that may be damaged. Especially vulnerable are bottom plates in walls insulated with batts, which may exhibit the so called "thatched roof effect" of condensed moisture trickling down the vertically-oriented fibers. Fiber glass is susceptible to air exfiltration, the major cause of moisture migration into walls and ceilings. Vapor retarders, air barriers, and careful caulking and sealing are necessary to prevent moisture buildup in walls in colder climates.