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There are less expensive generic filters that fit the Dreamstation. I've tried more than one of those brands and although some of the filters in each package I received worked well, several significantly impaired the air flow from the machine to the mask. Unfortunate, because the Philips Respironics filters seem to be priced excessively high IMO. But the point of CPAP is to provide proper pressure. If the less expensive filters interfere with the air pressure in detrimental way, I am afraid that we consumers have to pay Philips' price. Medically necessary breathing equipment must function properly. "Might work correctly" isn't an attractive option, even if the price is more reasonable.
These are the genuine Respironics filters, which I feel are important to keep your sleep machine running optimally. My sleep center gave me the Philips Respironics BiPAP with genuine filters installed obviously. What they gave me for filters were some off-brand with no markings. After just a very short time of using off-brand, I noticed my machine acting up.. Randomly shutting off at night, louder than usual. I installed these genuine filters and have not had a problem since. This is definitely one of those times where you should really go with the manufacturer brand.