The internal layer is made of heavy-duty dual aluminum foil that is fire/flame resistant. Its outer layer utilizes dual PVC thermoplastic that protects the aluminum from cuts and tears while stopping leakage. Each duct tube is held together by an internal steel-wire spiral that is flexible and easy to install in hard-to-reach places. Variety of applications: Suitable for any ventilation & air conditioning (HVAC) purposes, move and deliver air in kitchens (cooking exhaust), greenhouses and grow rooms (air circulation, intake, exhaust, and light fixture cooling), bathrooms (smell and moisture exhaust), grow tents and other applications.