These filters go with the ResMed S9™ Series CPAP machines. Filters are an imperative component of the CPAP machine. They collect dust, pollen, mites and other components that would otherwise make it into your lungs and disrupt sleep. It is recommended that CPAP filters are replaced or cleaned every 15-30 days depending on the unit. Select standard or hypo-allergenic filters. Select filters in a pack of 1, 2, 12, or 50.