This complete particle filter change kit fits all Blueair 500/600 Series (501, 503, 550E, 601, 603, 650E) and comes complete with:
3 standard HEPASilent filters of polypropylene (traps particles)

Replace every 6 months.

Easy maintenance:
When the filters need to be replaced (twice yearly), just open the lid, lift out the old filters and drop the new ones in. No screws, hooks or tools and less than one minute of your time are required.