The Philips Respironics DreamStation Disposable Ultra-Fine Filter is for use with the Philips Respironics DreamStation machines. Whenever it's necessary to be replaced you may just dispose it, since it's disposable. Being disposable, this filter can't be washed, it must be replaced. To your great advantage of not having to constantly buy more, the pack comes with six! Its main job is to block all dusts from ever entering the machine, being housed in the lighter blue frame.