Four-layer filter replacement keeps the Lorell HEPA 240 Air Purifier running efficiently. Pre-filter removes hair, lint and large particles and protects the HEPA filter. Activated carbon layer filters out odors, formaldehyde, volatile organic compounds (VOCs) and household fumes. HEPA filter removes up to 99.97 percent allergens and dust as small as 0.3mm. A second pre-filter removes large particles that made it through the first three layers and protects the fan.