You will receive a pack of 3 x 100mm / 4 inch plastic ducting connectors with inline backdraught shutter / gravity damper flap. Material: PVC plastic. Colour: white. Diameter: 100mm.Prevent cold air from entering through home exhaust fan ducting using back draught shutter. Efficient Airflow Control: Features of 100mm backdraught shutter flaps, designed to effectively prevent backdrafts and maintain optimal airflow in duct systems. Universal Compatibility: Suitable for connecting with 4-inch duct pipes or flexible ducting hoses, ensuring a snug and secure fit for a variety of ventilation setups. Durable Construction: Crafted from high-quality materials, these shutter flaps offer long-lasting performance and resistance to wear, making them ideal for both commercial and residential use. Easy Installation: Designed for hassle-free setup, these non-return valve dampers can be quickly and easily installed without the need for professional assistance. Cold Air Stopper: Acts as an effective barrier against cold air intrusion, maintaining indoor temperature and energy efficiency, especially during colder months., Manufacturer: NESVENT