The Final Primary System filter is a High Efficiency Particulate Air (HEPA) filter that captures any remaining particles regardless of composition. Because a True HEPA air purifier is excellent at trapping almost all airborne contaminants, it’s the best choice for someone who has asthma or suffers from allergies. This dense filter is amazing at trapping allergens such as dust, pollen, mold and pet dander. And, because these particles are trapped inside the filter, there is no way for them to re-enter the air space. This keeps your home fresh and clean.