Insulated, sound-absorbing aluminium duct with a coupling at each end. This silencer has an outer layer of plastic which means that it emits some noise to its surroundings. The ducts are supplied as compressed items. They should only be pulled out to their full lenght when they are fitted. Insulation thickness = 50 mm. Supplied as a compressed item, to be pulled out to 0.75 m or 1.5 m when fitted.