Review on PURBURG 4-Pack Replacement Humidifier Wick Filters for Vornado MD1-0002: Compatible with Multiple Models & Brands - Holmes HM250, HM405, HM406, HM725, and more! by Jason Hayes

I couldn't figure out why my Vornado stopped wicking. After all, there are few moving parts. Looking at other reviews of this and other products, I learned that the problem was that the filter only got a few inches wet. One reviewer suggested soaking them in hot water with white vinegar for twenty minutes. Haven't tried it yet, but I flipped the filters so the wet part was up and that seemed to help improve the humidity by a few percent. Therefore, some filters from this and other brands do not absorb moisture well, although most of them perform well.