This Backdraft Damper helps prevent reverse air flow when fans are disengaged, saving CO2 and preventing odors from flowing backwards. Contructed from galvanized steel, it features a rubber gasket pre-install This Backdraft Damper helps prevent reverse air flow when fans are disengaged, saving CO2 and preventing odors from flowing backwards. Contructed from galvanized steel, it features a rubber gasket pre-installed on the exterior to ensure an air tight seal.