Flexible Duct 25mm,50mm Insulation consists of sleeve, insulation and core. The sleeve is made from aluminum foil or Metalized PET, which can supply much higher fire rate, laminated with glue, and the core is made from metalized PET/ aluminum foil together with glue by encapsulating spring wire inside. It is used for the air supply or return in the air conditioning system connecting with the tuyere.