Product review (4 stars): Works great!!!  Save the cap from old filter!
Box comes with three replacement filter cartridges.  My box also came with some bonus swaps (for the essential oils tray); 10 very thin swaps about the thickness of fleece about 2 cm by 3.5 cm.  Be sure to SAVE THE FILTER CAP!!!  The image on the box shows the filter cap, but it doesn't come with one.  I was successfully able to replace the filter and able to continue the use of my humidifier.  Please note that filters only remove certain contaminates/minerals from the water.  These filters do not remove bacteria, so be sure to also properly clean your humidifier.