The Helios ELFBR 250 G4 is an in-line air filter box designed for ventilation systems using circular ductwork. Both ends have spigots with double lip rubber seals to ensure a tight fit with nominal size ducts. The durable casing is made from galvanised sheet steel. For ease of maintenance, the unit includes an access panel secured with a clamp for quick filter replacement. The filter consists of a synthetic fiber mat, classified as ISO Coarse 70% (G4). It is temperature resistant up to +100°C, meets fire safety standards DIN 53438 F1, is self-extinguishing, and can be regenerated 10 to 15 times. The filter offers a dust holding capacity of 122 g/m² to maintain effective air filtration.