Usually refers to antifreeze.
In the north, the antifreeze is ethylene glycol (propylene glycol or glycerol). Heat transfer media with different freezing points are selected according to different latitudes. In the area south of the Yangtze River,-10℃ non-freezing antifreeze should be selected. In the area north of the Yangtze River, antifreeze that does not freeze at -20℃ should be selected. In the area north of the Yellow River, antifreeze that does not freeze at -30℃ should be selected. Ensure that the system will not freeze in winter. Pure water is also used as heat transfer medium in Yunnan and other places.
I hope this answer is helpful to you.