A humidifier tub for a respiratory apparatus is configured to deliver pressurized breathable gas to a patient's airways. The humidifier tub includes a base and a side wall defining a reservoir for containing a supply of liquid to be evaporated. In addition, the container is made of a first material. The humidifier tub also includes a heating element provided inside the container and covered by a layer. The layer includes a second material different from the first material.