These are disposable replacement M-Series fine filters from Respironics. They fit in all of Respironics range of M-Series machines. Respironics advises that the fine filters should be replaced every 30 days, or if the filter is dirty or torn. When replacing the filters, put the filter into the machine first with the mesh side facing into the machine. Then, insert the black filter on top of the new white filter.
For the Respironics M-Series User Guide, please click here