Catit Magic Blue Filter is 25 times more effective than activated carbon filter, free of chemicals and easy to use. Better air quality is ensured in closed litter boxes and in the surroundings. This unique filter can be used in ALL closed It just needs to be installed in the door with the included container with the filter in it. The filter itself can be replaced, so you only need the container once. The pad absorbs the unpleasant odors like a sponge instead of drowning them out like chemical air fresheners.The filter reduces the ammonia smell by up to 80%. At the same time, the excrement smell is reduced by up to 40%, depending on your cat's eating habits. This filter is a great alternative to toxic and chemical air purifiers