Sheet metal is the most commonly used of the four duct materials found in homes and commercial buildings. Constructed from galvanized steel or aluminum, rigid sheeting is the most durable and has a smooth surface that is generally easy to clean. However, it can trap dust and other particles, so it's a good idea to have the ducts professionally cleaned periodically to maintain optimal air quality. Fiberboard is made of fiberglass threads held together by resin and is less likely to be affected by mold due to its non-porous surface. Flexible air ducts are usually cube-shaped and have no elbows or deviations.
They are composed of a coil of metal wire covered with a layer of flexible plastic and have thermal insulation made of glass wool, polyethylene or metallized PET. This type of duct is preferred in tight spaces where other types are difficult to install. Rigid-type ducts can also be coated with fiberglass. These are similar to sheet metal ducts but have an inner or outer fiberglass lining. This type of air duct is preferred in commercial buildings and offices, as it has the ability to dampen the sound of air conditioning. Fiberglass air ducts are similar to fiberglass lined ducts, but they are sealed to ensure that no fiberglass particles come off.
These types of ducts are more prone to the formation of mold and bacteria due to their porous surface, so they require intensive cleaning that can make them less durable. Different air duct materials have their own advantages and disadvantages, but sheet metal is usually recommended since it is not porous by nature and does not allow mold or bacteria to spread in air ducts. The overall design of the air duct system also plays a critical role in system performance.
