Honeywell FC100A1011 20 x 20 x 4 replacement media air furnace filter;

Honeywell says: Our filters are up to 4 times more effective and is up to 85% more efficient at capturing airborne particles compared to a standard one-inch filter. They captures both microscopic particles like dust and smoke in addition to larger contaminants such as mold spores and pet dander. Our filters last up to four times longer than a standard one-inch furnace filter. Replace them every 6-12 months versus monthly or quarterly changes.