Product review (4 stars): HC-14 Humidifier Filter
Exact Honeywell replacement filter - nothing different than the one that came with the humidifier.

I will caution you on this (and why I gave it 4 stars) - the filter is very susceptible to tearing when wet so you MUST handle it carefully when rinsing it out.

Here is what I found works best.  I take the filter out by grabbing the blue outer edge (stronger than the white inner part) and flip it over and place it carefully in a bucket of clean water every 2 days.  I let it soak for about 10-30 minutes then place it back in the humidifier.

As it runs, the water leaves minerals near the top of the filter and it gets really stiff.  Flipping it helps keep the filter flexible and provide a good wick for water.

The soaking helps loosen the minerals and other funk that is left behind when the water evaporates.

Doing this, I use one filter all winter long unless bacteria starts to grow (stinky smell) and then I soak it in a bucket with chlorine from the hot tub to kill the nasty bacteria.  Smells like a pool for a few minutes afterward, but at least it is clean then.

I run my humidifier 24x7 and have good water so you may have to adjust your schedule of filter maintenance.