The Helios FSD 400 is a sturdy flexible duct made from aluminium casing. Its perforated inner surface securely holds a mineral wool lining approximately 58.5 mm thick, offering excellent sound insulation. The duct has spigots on both ends for straightforward connection to other ducts or secure attachment to fans using a pipe clamp connector (BM). This duct has a pressure drop about four times greater than that of standard rigid ducting.