True HEPA Air Purifies Actually Work Better When Dirty

This is one of the main differences between True HEPA air purifiers and others. This is also where the terms "True" and "Absolute" become interchangeable. An absolute type filtration media is designed to be more effective when dirty than when clean. The addition of the trapped particles actually increases the filtration power of a true HEPA air purifier. The reason for this is actually quite simple. As the dirt builds up, the spaces through which the air can pass become smaller.