Product review (4 stars): Info about blue vs white filters
I am writing to address the issue of the blue vs white filters. I ordered a second filter directly from Honeywell, due to the complaints on Amazon,  and it was white -without the blue prefilter outer layer.  So I promptly emailed Honeywell and was given the courtesy of a quick response. They told me that Honeywell no longer makes the filters with the blue outer layer. The white layer is supposed to give more humidity.
  I have found this to be true, however, the blue outer filter really filtered out more small particles from the air. We have multiple pets so this was an important feature for us.
  Also some people are having a bacteria/mold issue. 4 drops of tea tree oil in each water tank nightly will eliminate any problem. Begin with a clean tank, of course.
  Another thing I do is flip the filter nightly so all of the mineralization does not end up in one spot and clog the filter. One last maintainence trick - as another reviewer said - wash the base with white vinegar on a regular basis and let your filter soak in a vinegar water bath to remove the minerals.
  Last year I only needed two filters for 6 months of use. Cannot say about the all white filters -will update at end of season.
  I do think the filter price is quite a bit too high for what you get now. Still love my Honeywell humidifier!