A flame-resistant, insulated, plastic HVAC duct including a channel configured for conveying forced air and a duct wall forming the channel, the duct wall including a plastic layer disposed between a thermally insulating layer and a metal foil layer. The metal foil layer is arranged to form an outer surface of the duct wall, and the thermally insulating layer is arranged to form an inner surface of the duct wall. A second metal foil layer may be disposed between the thermally insulating layer and the plastic layer.