Citizen Industries Limited manufactures Filter Top Animal Caging System. Citizen Industries Limited manufactures Fan Coil Units and Air-Conditioning Equipment for domestic application. The Filter Top Animal Caging System consists of a cage box, depressed grill and a wire or plastic structure on the top of cage with filter element. Similar to open cages, these cages are also housed in the standard racks installed in clean rooms. The filter top protects the animals from environment contamination and also eliminates the spreading of infection from the cage to surrounding environment.