The fibrous glass duct system is normally made up of nominal four foot (1.2m) modules which are fabricated from 1, 11/2, or 2 in. (25, 38, or 51mm) thick, flat fibrous glass duct board stock having a factory-applied reinforced aluminum exterior air barrier finish. Duct system modules are fabricated using either specially designed hand tools or grooving and closure machines. These modules may have factory shiplapped male and female ends which assure close-fitting, smooth joints when duct sections are joined. Ducts with spans up to 96 in. (2.4m) may be constructed when proper reinforcement is used. Duct fittings such as tees, offsets, elbows, and transitions are also fabricated from these modules or from flat duct board. Equipment such as electric or hot water in-line heaters, manual or powered volume dampers, registers and grilles, diffuser drops, and access doors may be incorporated into a fibrous glass duct system. Fibrous glass duct boards are available with a durable interior surface treatment to enhance cleanability when NAIMA guidelines are followed.

Fabrication tools are available to produce ten-sided (essentially round) fibrous glass duct modules. Preformed round fibrous glass duct is also available in a range of diameters and wall thicknesses up to 2 in. (51mm).