Product review (2 stars): Not an Emerson HDC-12 Filter!
Plastic ribbing is on both sides of the filter like another reviewer mentioned.  This means it will not fit in curved filter holder of the Emerson humidifier.  I hate returning things so I took some scissors and cut it in about 5 spots on one side and jammed it in.  Needless to say I'm not thrilled.  Will buy this product from somewhere else next time.