The Avalon Replacement Filter is suitable for the models A1HUMIDIFIERWHITE and A1HUMIDIFIERBLACK. The filter is easily screwed onto the tank screw cap. Simply unscrew the old filter and replace it with a new replaceable one. The filter is made of ceramic balls which filter out unwanted minerals and bacteria in the water. It also reduces the limes in the water. By replacing the filter every 6 months, the lifetime of the humidifier will be extended.