A 20x30x1 air filter is a common size of air filter used in heating, ventilation, and air conditioning (HVAC) systems. These filters are designed to improve indoor air quality by capturing and removing various airborne particles, such as dust, pollen, pet dander, mold spores, and even some bacteria and viruses. The dimensions 20x30x1 indicate that the filter is 20 inches in width, 30 inches in height, and 1 inch in thickness.