These furnace humidifier filters are soft, spongey filters that fit nicely into the WB2-17 Humidifier supplied by Lennox. Like any humidifier filter they are at their best when you aren't thinking of them. In other words, you want them in place, so the furnace doesn't dry out your house.I had a handyman come out to resolve a furnace issue, and he did something I never had done, he checked the humidifier and found there was never any water running to it. He replaced the original, but unused filter with this one and restored water to the humidifier. The house already feels much more comfortable and less dry.If you have the appropriate furnace humidifier do yourself a favor and keep these in stock. You should be good to go if you replace them at the start of each new heating season.