The Helios FSD 250 is a robust flexible duct made from aluminium casing. It features a perforated inner surface that holds a mineral wool lining approximately 58.5 mm thick, which provides excellent noise insulation. The duct includes spigots on both ends for straightforward connection to other ductwork or secure attachment to fans using a pipe clamp connector (BM). Its pressure drop is about four times greater than that of comparable rigid ducts.