Hello Minimee1, the filters are necessary so that OSKAR can humidify the room air - without filter mats, no water evaporates, i.e. no moisture gets into the air.
Please do not hesitate to contact us if you have any further questions. Your Stalder Form Team

That's not true. I bought the Oskar and I'm sorry to say that it doesn't get much more unhygienic than that. I don't want to advertise other products. But the Oskar and its stinky and extremely expensive filters go down the drain after 2 weeks. 90.- for the cat but better than breeding bacilli! Or use it without a filter. The filters only bring the water centimetres closer to the propeller. Evaporation takes longer without a filter, but water is definitely evaporated.