What are the main heat transfer fluid categories?

In a heat exchanger, heat moves from the heat source into the moving fluid through a thin film of fluid.
If the temperature of this fluid film exceeds the maximum recommended film temperature, the chemical bonds holding the molecules together start to break apart, the fluid will degrade, and the fluid life might be shortened.
In the circuits, thermal cracking will cause deposits formation, pump cavitation and loss of heating capacity.

The ISO 6743-12 standard establishes the detailed classification of family Q (heat transfer fluids). 
Temperatures indicated in the table are those of the bulk fluid, measure in the discharge line from the heater. Film oil temperatures may reach higher values.