No. The heaters are in a sealed sleeve. However, the heater sleeves should be kept away from any contact with water. If the sleeve is damaged then you must activate the heater with water and dispose of the heater/heater sleeve. Care must be taken because of the steam and heat being generated when the heater is activated. If you open the heater sleeve and decide not to use it immediately, humidity can get in and the heater might not function to its full capacity. It is considered inadvisable to open the sealed sleeve and not use it immediately.