Product review (5 stars): Perfect Filter Replacement for Vicks (Be careful on which cleaner to use, see review and don't do what I did)
This filter is perfect for replacing old/damaged filter on Vicks model. Which brings me to mention what NOT to do with these humidifier filters...

Mine looked dingy and I was concerned about mold...also the filter tended to dry out at the top and sometimes would stop absorbing the water.
So, I removed the filer and spritzed a mist onto the filter which was a diluted mixture of bleach and water. I pumped a few sprays from a cleaner bottle and let the filter sit in a bathroom sink for a few hours, then filled the sink with water, and rinsed the filter out. At this point, when I began to rinse the original Vicks filter out, it disintegrated in my sink. It literally just broke apart into extremely tiny pieces and started going down the drain.

It took me a good long while to find the information online for the Vicks filters and humidifier, but the online information attributed to Vicks said it is normal for the filter to turn brown and not to do what I did (using bleach on the filter).  I bought this replacement filter so this unit would not be totally worthless...but...I also another Filter-less humidifier which was also from Vicks and houses the vicks vaper packs and will also do essential oils...it is larger and produces a ridiculously large volume of humidity in a short period of time! I believe the model number was 4500 on the newer one if anyone should need it, but the old unit works as new with the new filter as well.