Air Conditioning Heating Understanding Ventilation Systems Types of Air Ducts January 29, 2010 by admin Air ducts are used to distribute air through out a building, or to exhaust air outside of a building. The most common are: sheet metal, fiberglass lined, fiberboard, and flex-line air ducts. Sheet Metal Air Ducts The most common type of ridged air duct is constructed of galvanized steel or aluminum. They may be round, […] Read more » Fiberboard Air Ducts Fiberglass Air Ducts Flexible Air Ducts Flexline Air Ducts Insulated Air Ducts Sheet Metal Air Ducts