Cloud point is an important quality specification for diesel fuels. This is an indicator of the tendency of a fuel to form wax crystals when cold. These crystals can clog the atomizer that injects fuel into the combustion chamber of a diesel engine.
Cloud point is measured as the temperature at which long chained paraffins begin to crystallize, causing the fuel to turn cloudy.
Cloud point specifications are a maximum temperature. A material with lower cloud point is more desirable. In general, low density (lower boiling point) material will have a lower (more desirable) cloud point.