These registers filter out dust and particles from the air that is blown out of the central heating and air units. It works in conjunction with the intake filter insuring that the air you breath is purer and fresher. It is a Utility Patent, good in China, Australia, Canada, Mexico, and the U.S. and covers all applications in the residential, commercial, automotive, and aircraft fields. This patent expires in 2021. Call 865-357-8128 for more information