Product review (5 stars): Humidifier Filters
I have been using the Holmes filters for my humidifier for at least 10 years.  I can order it online and shipment is quick.  I actually use one filter per winter season when my house is too dry (I live in the Northwest where it is damp all winter long.).  I run it for about 8 hours a day during the week and longer on the weekends. I toss it at the end of the season and order a new one, so that I have it ready for the next year.  You can visually see when the filter is ready to discard. The life of the filter depends on the water quality where you live and the hours you run your humidifier. This filter is encased by a metal "cage" that helps it stand erect, so when it is saturated with water it does not wilt. I highly recommend this filter.