4" External Gravity Flap Backdraft Shutter - White The introducing the 4" External Gravity Flap Backdraft Shutter in a clean white finish. Engineered with a gravity flap design, this shutter effectively prevents backdraft in ventilation systems, ensuring optimal airflow. Its external installation design allows for easy mounting on external ventilation outlets. Crafted with durability in mind, the white color adds a sleek look while resisting outdoor elements. Versatile and compatible with various ventilation systems and extractor fans, this backdraft shutter is an essential component for maintaining efficient airflow in your space. Features: