Air conditioner grates and grilles, also knonw as diffusers, are generally made of metal. The TruAire line of products is made of steel, including the frame, blades and dampers. Some manufacturers incorporate friction-reducing technology to keep the system quiet and relatively free of rattles.
Most air conditioning grilles feature a lever that allows for the movement of dampers in the mouth of the ductwork. The purpose of these is to control the direction and amount of airflow coming into the space. The use of steel minimizes corrosion that can occur through exposure to moisture in the area, as well as dust particles and other debris.