Unlike standard cab filters that have only a paper-like medium to trap dusts, this three-stage filter combines dust filter mediums (Stage 1) with activated charcoal (Stage 2) which adsorbs pesticide and other organic vapors and traps pollen and molds. A final filter (Stage 3) reduces the amount of charcoal fines entering your cab, so you breathe cleaner air. Each filter is housed in a durable metal case and is designed to fit snugly in your tractor cab. Replace filters annually or when you begin to again taste or smell chemical vapors.