Longitudinal and transverse joints of fibrous glass duct modules are sealed using one of three UL 181A listed closures:

• UL 181A, Part I (P) - Staples and pressure-sensitive aluminum foil tape. 21/2 in. (64mm) wide tape may be used in making closures with 1 in. (25mm) duct board. 3 in. (76mm) wide tape is recommended for 11/2 in. (38mm) duct board, and is mandatory with 2 in. (51mm) duct board.
• UL 181A, Part II (H) - Heat-activated aluminum foil/scrim tapes, 3 in. (76mm) wide.
• UL 181A, Part III (M) - Mastic reinforced with 3 in. (76mm) wide glass fiber fabric (scrim). This closure system may be required when the system is part of a fire-rated assembly.