This pad fit my humidifier very well.  I will warn you, I was tempted to buy one of the 10x13.5" filters just by visual inspection, so be sure to measure your existing pad before you order (the owners manual does not have any measurements in it because they want you to buy it for a ridiculous price from your HVAC dealer)!  I measured the item before ordering it and had no issues.  It is about 1/4" larger than what I measured (which is as described), but that is to allow the notches in the filter housing to hold the filter in place.  Despite not being mentioned, this is an aluminum pad which should last for about two heating seasons.  To replace the pad, just open the door on your humidifier, slide out and dispose of the old one and replace it with the new one.  I will update this review if I have any issues.  The seller shipped very fast as well.  Good experience overall.