Product review (1 stars): These must be knock-offs. They do not "wick" the ...
These must be knock-offs.  They do not "wick" the water as they are intended to do on the model 400.  It needs true evaporator panels,  They did not work at all.  They stay dry the whole time, there is no water absorption being done which is how the model 400 works.  I also confirmed with Aprilaire that the official panels will have marks for top and bottom, these did not and Aprilaire only sells to dealers so not sure why the amazon listing says 'aprilaire' as the seller.  Also, not sure what all these comments are that say these "work"?  How are you testing that they work?  Yes they fit, but how is the humidity in your home?  These do not "work", but yes they fit.  Also - these are not filters...  in the model 400 the water is supplied from the top, and works via gravity, the water trickles down and then this is supposed to wick it back up so that it stays moist, and the blower blows the moist air into your home.  These do not - water sits on bottom, air is none the moist'er going into your house.