Air Cleaner Filter, For Evaporative Humidifiers, 2 Stage Filter Is Made With Highest Quality Of Materials, An Electrostatic Layer Traps Airborne Particles, While A Carbon Layer Traps Smoke & Odors, For Use With Aircare/Essick Air Models 427 300, 447 400HB, 4D7 Series, 4DTS 300 Series, 696 Series, & 697 Series.