Fragrance. Air flow. Simply attaches to any furnace/AC filter. Contains one air freshener. Search for scent. Attaches to any air filter for rich aromatic whole home fragrance. Simply attach Filter Fresh to any size air filter on central furnace/AC units. Larger homes may require two pads for more effective fragrance. Other uses include scenting small areas such as bathrooms, closets or vehicles. Or, hook Filter Fresh to the front of an oscillating fan to scent one room at a time.