The Cape Backdraft Damper is the ultimate one way air flow valve, designed to overcome the inefficiencies and limitations of traditional gravity or butterfly dampers. The Cape Damper consists of a specially formulated fabric sleeve attached to an outer metal sleeve. The fabric sleeve will allow air to pass through in the desired direction of flow with miniscule reduction in airflow. For reverse airflow, airflow that should be stopped by a backdraft damper, the Cape Damper gives a better seal at a lower pressure and holds that seal as the pressure increases. The Cape Damper is quiet, with no metal clanging sounds, and can be installed in a horizontal or vertical orientation. It is available in two sizes, 4" and 6". Best installed horizontal position.