Product review (4 stars): Purchased for Vick's Cool Mist V3900
Purchased for Vick's Cool Mist V3900.  The filter fits VERY snugly on the unit.  Works fine but have to snip top and bottom for it to fit better.  Have purchased filters at Walmart (don't know brand) in the past for more $'s and they fit VERY loosely.  For the price it's worth a little work.