Unlike some CPAP machines that use two filters, the Luna 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 on this page is supplied standard with all Luna II Series CPAP devices. The white ultra fine filter, available elsewhere on this site, is an optional alternative for customers who need additional filtration capabilities in a disposable filter. DO NOT use both filters at the same time in your Luna CPAP. For complete instructions review the documentation that came with your equipment.