1.[Compatible Models]The package include 3 Pack 500/600 Dual Protection Filter true HEPA Replacement Filter Compatible with Blueair Classic 500/600 Series Air Purifiers 501, 503, 505, 510, 550E, 555EB, 580i, 601, 605,680i. NOTE: PLEASE MAKE SURE YOUR AIR PURIFIER MODEL BEFORE PURCHASE!!! 2.[Dual Protection Filter]Our Classic 500/600 Series for Blueair Air Purifier designed with Dual Protection Filter System, include H13 true HEPA filter made of high-quality non-woven fabric and activated carbon filter, is durable and long-lasting, allowing the 500/600 Series filter to last longer, bring convenience and fresh air in your life. 3.[H13 True HEPA Filter]Classic 500/600 Series Dual Protection filters for Blueair Classic 500/600 Series with high efficiency H13 True HEPA filtra-tion system, can attach 99.97% of particles as small as 0.3 microns in size, such as pollen,dust, pet dander, household dust and small particles. The activated carbon filter is more effectively to attach smoke, cooking smells, pet odors, VOCs and other household odors to keep the air clean around you and your pets. 4.[Easy to Replace and Install]Simply take out the older and dirty filter and replace NEW Classic 500/600 Series Replacement Filter. The side of HEPA filter need facing fan when replace (The package with the indicator note 'Facing in' on the top of HEPA filter side). Recommended to replace 500/600 Dual Protecttion Filter every 6 months depending on usage for optimal performance.