Product review (3 stars): So-so filter, but that's humidifiers for you...
Pretty much if you own a humidifier this fits, you're going to be buying a lot of these.

The outer black netting is just black colored cellulose, like the inner layers.  There's nothing special about it, except for the color.  After just a few weeks of use, it's already starting to fall apart in spots.

Humidifier filters get really disgusting really quickly.  I recommend replacing the filter at least once a month, so keep that in mind.  If you live in a not-hospital-clean household, plan on picking up some antibacterial agent and keeping tabs on the state of the filter.  Cleaning the humidifier once a week or so is also a must.  Flip the filter daily.  These things grow bacteria and other disgusting stuff in days if they aren't properly maintained.