BLUEAIR Classic 500/600 Series Genuine Dual Protection Replacement Filter; fits Classic 580i, 680i, 501, 503, 505, 510, 550E, 555EB, 601, 605 (3 pack)

Yes, they are pricey. Other, cheaper brands of replacement filters may claim to be compatible, but you will be compromising the performance of the unit and may even damage it.I'm not a shill for BlueAir, but we own 7 of their filters and they work great.It's important to understand BlueAIr units do *not* use HEPA filter media, but they *achieve* HEPA filter media performance using a unique combination of an ionization chamber where air is drawn into the unit (imparting a charge to particles in that air) and a filter media which builds up an opposite charge from the friction of air molecules passing through the media. The opposite charge attracts the charged particles in the air stream and binds the particles to the filter media, removing them from the air stream which then passes into the room.This means the unit *as a whole* removes just as many impurities as a HEPA filter, while providing a much higher clean air delivery rate (CADR) over a wider area than a HEPA filter, as HEPA media greatly restricts the airflow due to the high density of the media.Additionally, it is harder for the fan in the unit to push air through denser HEPA filter media, creating back pressure which causes excessive wear on the fan motor.All I can say is our BlueAir units are still going strong after over 20 years of continuous, daily use using authentic BlueAir replacement filters. We've also had some HEPA filter units which took longer to clean the air, only improved the air quality in a portion of a room, were much noisier and eventually became unusable after a few years due to fan motor bearing failure (which made them very noisy, even though they technically still functioned), or the lack of availability of replacement filters.

Quality of these replacement filters are second to none. Definitely buy the name brand filter it’s a mistake not to. Keeps smells down and room cleaner. They are low noise and perform better then the knock offs. Performance wise these are the ones you want.

I tried an off brand filter which had an unpleasant odor and did not get rid of kitchen odors in living room. I went back to the original Blue Air smoke block filter (which works great for allergies also). More expensive, but worth it in my opinion. This filter clears out kitchen cooking odors and light smoke from frying. It also works well for reducing airborne allergens. I have a 750 sq ft living/dining room area which the Blue Air 605 works great!

This is the 3rd time that I have ordered this set of three filters. They have worked very well in the air purifier, which requires three filters. This time Amazon sent only one filter, despite the product description of "three filters". Amazon replaced the incorrect item with, again, only one filter. So it is a very good item, but only if you can get a full set.

Blue air, classic, dual protection filters really work. I live in a dusty prairie community, where summertime pollen and fire and wildfire smoke are a daily issue. These filters are our final level of defense after HEPA filtering all of the incoming air to our house as it circulates the, six month change interval works even under these conditions. Of note: I received very professional and thorough assistance from Amazon when an issue issue. Issue a rose. with shipping. I especially appreciate the help because these filters are sometimes hard to get and the substitute generic types do not seem as effective, especially with smoke. Thanks