Unlike some CPAP machines that use two filters, the Luna G3 Series uses a single filter -- either reusable black foam or white ultra fine -- to filter out particulates in the air as they enter the CPAP. The reusable foam filter, available elsewhere on this site, is supplied standard with all Luna G3 Series CPAP devices. This disposable white ultra fine filter is an optional alternative for customers who require additional filtration capabilities. DO NOT use both filters at the same time in your Luna CPAP. For complete instructions review the documentation that came with your equipment.