The Airbox 4+ carbon filter is 100% airtight and easy to setup, use, and maintain. With 12″ flanges and a CFM of 3500 these units fit into all ducting and filtering systems. They utilize 100% premium virgin coconut charcoal and feature replaceable high-flow filters which use 100% of the available surface area, for optimum performance. Great for commercial or residential use. (1) pre-filter included. Made in the USA.