Bionaire Odor Grabber Filter Pack Set, 2 sets/pack Foam Pre-Filter traps litter dust, dander and fur to reduce air particles Odor filter contains activated carbon which is charcoal treated with oxygen to open up millions of tiny pores that adsorb organic odors Odor filter also contains Zeolite which is a natural mineral with a structure of pores and channels especially useful in removing ammonia-based odors