21-1/2 x 23-1/2 x 1 Electrostatic Washable Permanent A/C Furnace Air Filter 21-1/2x23-1/2x1 Traps 95% of airborne dust and allergens Permanent & Washable - Just hose off and reinstall Replaces disposable furnace filters Lifetime warranty Self-charging electrostatic filter media - does not require electricity