The ceramic element prevents the formation of what is called «white mist,» a common problem with ultrasonic humidifiers using metallic vibrating element. (mymilkybaby.com)
The MistAire XL is a beautiful, well - built ultrasonic humidifier that is capable of delivering a huge amount of mist very, very quietly (so there is no need to worry about it waking up the kiddies). (wetheparents.org)
The reason being that ultrasonic humidifiers emit a fine white dust. (momtricks.com)