Product review (3 stars): Sponges are fine, the humidifier they go into sucks.
These filters are basically sponges. They are an important part of the humidifier unit that they go into because without them, the humidifier can not function (the sponges increase surface area which increases the rate of evaporation - causing humidity in the room).

These are called replacement filters because the ones that come with the product break (they have a natural life span to them). As they are used, they are repeatedly hydrated and hydrated. This causes the porous surfaces in the sponge to break. Eventually, the bottom part beaks off from the top and the top stops hydrating.... leading to a less efficient or non-functioning humidifier.

I don't recommend the humidifier that these sponge filters are for because of the noisy fan motor. For that reason, I am leaving them three stars. If not for the humidifier, I have no complaints about these sponges.