Mat-Faced Micro-Aire® duct board is produced from strong glass fibers, bonded with a thermosetting resin. The airstream side of Mat-Faced Micro-Aire duct board features a black fiber glass mat, which minimizes visibility of the duct system at supply air and return air outlets while providing excellent durability in high-velocity conditions. The exterior surface features a fire-resistant foil-scrim-kraft facing extending the full width of the male edge to serve as an integral closure flap for section joints. Mat-Faced Micro-Aire duct board is molded with double-density, male/female edges for secure connections.