They are available in generic versions or the ResMed brand for customers that prefer OEM filters. The Spirit Medical and Med-Dyne brand filters are replacement filters of equal quality to the OEM versions. They are available in packs of two with quantity discounts when ordering packages of 6 or 20. The packages of six will ship as 3 packs of two and the package of 20 will ship as 10 packs of two. The Standard filters are a two stage blue and white mesh. When these filters are installed correctly the blue mesh should be facing out. These filters should be replaced monthly under normal conditions.