Product review (5 stars): Never got to use the replacement pads
I own the HWM-450 humidifier.  Or maybe I should say "owned."  It worked very well for me for most of two heating seasons, then went belly-up abruptly--right after I received (but never used) the replacement absorption pads.  The original pads, which I'm pretty sure are identical to the replacements, worked very well.  I found they could be re-used several times if soaked in vinegar and rinsed.  They definitely seemed to help extend the time between cleanings.