Here we discuss the use of laser diffraction for measuring the particle size of extenders. The practical relevance of this particle size data is explored with reference to the experience of Viaton Industries, the UK's largest manufacturer and processor of barium sulphate functional fillers and extenders. Viaton Industries uses a laser diffraction particle size analyzer to ensure efficient milling and one aspect of the company's work is the production of extenders used in coatings with specific gloss/gloss retention properties.