The Stadler Form O-030 Oskar humidifier replacement filter 2-pack is constructed of antibacterial treated paper. It is made especially for use in evaporator systems like the Stadler Form Oskar evaporative humidifier. This filter transports water to be naturally evaporated into the air. It keeps the cold steam free of minerals and other contaminants and keeps your humidifier operating at optimal levels. To keep your air clean and comfortable, it is recommended that this filter cassette is replaced every 2 months. The Stadler Form O-030 Oskar humidifier replacement filter 2-pack includes 2 filters in each package and doesn't require any cleaning.