This Architectural Drazwing is AutoCAD 2d drawing of Transition duct with insulation glasswool details in AutoCAD, dwg file. Fiberglass insulation is the most common type of air duct insulation on the market. R-values range from R-4 to R-11 for ductwork. Fiberglass insulation comes in two distinct formats: flexible or rigid. Flexible fiberglass insulation for air ducts wraps around ductwork.