Product review (2 stars): Short working life
these days it's hard to find filters that fit my old Kenmore.  The Sears store rarely has them in stock so this is about the only kind I can find that will fit.  The Pro--they are cheaper and I dont' have to make a trip to the nearest store to get them.  The con:  they don't last long.  The original brand type were composed of solid strips of paper in a pleated format.  One set would last an entire season.  These have to be replaced more often.  My last set was installed in November and I just ordered replacements.  They gradually stop working.  I'm not sure if they become clogged with residues or what, but at some point you realize the humidifier isn't putting out very much moisture and when you reach down in and feel the filters, the top third or so will be bone dry. ( fyi, my water is not particularly hard--I have no issues with iron stains nor do I need to use extra detergeant, so that's not a contributing factor.)  I've tried turning off the humidifier and pouring water over them to try and get them wicking moisture again, but it seems like once they dry out and stop absorbing, you can't get them to work again. Once you notice that they have become discolored it's time to be ordering replacements.  Next year I plan to purchase the solid paper type--if I have to replace these 2-3 times in one year they wind up being more expensive in the long run.