Completely flexible thermally insulated air ducts, which supply to carry the conditioned or free air coming from the main channels and distribute them to places, consist of an inner duct, a bronze covered spiral steel wire inserted into it, a fibreglass reinforced outer jacket and a glasswool layer replacing between them. They can be easily attached to round and oval connection parts with metal or nylon clamps. Aluminium foil tapes are used for air-tightness at connection points.