When paraffinic hydrocarbons, which may form part of a distillate fuel are cooled, n-paraffines come out of solution by forming wax crystals due to limited solubility of the fluid. De temperature at which a cloud of paraffin crystals first appears, is known as the Cloud Point.
The degree of crystallization of the paraffines in the product correlates with the "cold energy" delivered to the sample. The crystals are finely divided particles which scatter and absorb light or other electromagnetic radiation. The scattering depends on the number of particles, the difference in refractive index between the liquid and solids, and the wavelength of the light. Those crystals can cause blockades, irregular operation and complete breakdown of the fuel system of diesel engines or heating applications.

The continuous determination of the Cloud Point temperature is being used for:

• Adjustment of the distillation range of the distillation tower slanting by:
  -   Manipulation of the final boiling point and the side stream flow
  -  Optimization of the refinery operation
• Manipulation of blend composition of different product flows.