Product review (1 stars): you need the plastic frames and they're not available
These filters no longer come with the plastic frames, which are no longer available through any other source.  Such a shame, because the new filters really don't work, drying out in a week or two in the humidifier, whereas with the frame they last at least a couple of months.  Fortunately I still have one set of plastic frames, so I stuff the filters in the old frames, which seems to work.  I won't buy another humidifier that uses just a bare filter - they really don't work.  A great product - the Bionaire W9 whole house humidifier -  now rendered ineffective by the business decision to sell more but inadequate filters.