This part of ISO 23900 specifies a method of assessing the degree of dispersion of a colorant in a thermoplastic polymer.

The method is suitable for testing colorants in the form of colour concentrates in all polymers used for extrusion and melt-spinning processes.

The filter pressure value (FPV) determined according to this method is valid only for the equipment, conditions and test polymer being used. The use of test conditions differing from those specified might give different results. The method of preparing the colour concentrate is not specified in this part of ISO 23900. The results obtained for individual colorants are therefore comparable only when the same method of preparation for colour concentrates is used.