Plastic gravity shutters prevent unwanted reverse airflow through external ventilation openings when the fan is switched off. Lightweight louvres open automatically under positive air pressure and close by gravity when airflow stops, helping reduce draughts, weather entry and pest access. Manufactured from durable UV-stabilised plastic, the shutters are corrosion resistant, easy to install and well suited to bathrooms, kitchens and other residential or light-commercial extract systems.