The Defensor PH26 employs the evaporator principle. This specifically involves dry air coming into contact with a mat saturated with water, absorbing this water and then being emitted into the room air in a practically germ-free condition. Air is thus humidified both inexpensively and with a minimum energy requirement. A further potential for active air improvement is to be found in air cleaning. The Defensor PH26 can be converted simply and is, in effect, a combination of both humidifier and air cleaner in one.