Insulated flexible ducts with metalized jackets are used in the HVAC industry for supply air, return air, and exhaust air transport where air conditioners, heaters, and ventilation applications exist. Such ductwork maintains good air quality, comfort, and prevents costly inefficiency. The inner polyethylene tube with reinforced wire coil gives strength and keeps the air inside the tube. The thin metal jacket keeps moisture and condensation from getting on the insulation, and the flexibility allows the duct to curve if necessary. The insulation in U.S. insulated ducts is typically glass wool or fiber glass.

The size of the fitting on the heater, AC unit, etc. will of course determine the needed duct diameter, and the length is normally cut by the installer. It is ideal to keep the distance short since a certain amount of pressure will be lost by air while it is travelling through the duct, and sharp bends and kinks also are avoided. The flexible ducts attach to the rigid sheet metal ductwork, to the AC, the heater, or have open contact with outside air.

Each duct has an “R” rating for its insulating capacity- for example, R6 ducts do well up to 200 degrees, and has one third more insulation around it than an R4. The greater insulation, the greater efficiency, but also the more one pays for the product. Wherever relatively hot air is present in the duct, especially if traveling through space with extremely lower temperature air in it, it is most important to have a high R rating. The cold air return to a heater would not need as great an R value then as the supply duct. The opposite would be the case with a split AC unit since the hot air is traveling outside, and the cold air is moving into the building. Another possible application for a high R duct would be a clothes dyer exhaust tube.

While the metal jacket keeps out moisture, there are also versions of metalized jackets, e.g. one line of ducts’ “silver jacket” feature, that are effective in noise absorption
as well. Clearly these would be more crucial when the duct goes through or near oft-used rooms- not so much in a little visited basement on the other hand.

Another special flexible duct is one with a heavy black jacket of polyethylene and UV light elements built in. They are commonly referred to as mobile home ducts for their due to their increased usage for this type of construction. This duct is particularly suited for use outside, though if in a well-lighted room, it could be useful indoors as well.

Insulated flexible ducts with metal jackets come in numerous standard sizes for different sized heater, vents, and ACs- some are even designed specifically for mobile homes. They install easy enough over round or oval fittings and can be easily cut and taped if one has the right equipment and a little experience. However, choosing the right R level for each duct and looking for special metal coatings that resist fire better or reflect light better, etc. often requires professional advice or services.