A flexible, sound-absorbing duct intended for supply and exhaust air systems in residential buildings. Its properties include sound attenuation, diffusion tightness, flexibility, adaptability, and flame resistance. The silencers are composed of a layer of profiled aluminum strip, glass wool, age-resistant PE plastic, and, for certain markets, a fiber cloth. They are supplied as standard with female (muff) connections at both ends but are also available with male (nipple) connections. They are produced in standard lengths of 600 mm and 1200 mm, in diameters ranging from Ø80 mm to Ø315 mm. The bending radius can be calculated at 2–3 times the diameter. The aluminum tube is classified as non-combustible, and the glass wool is VIM-inspected and also classified as non-combustible.