Paper consists of not only cellulosic fibers but also considerable amounts of mineral fillers. Fillers are highly desirable in printing papers because they increase the light scattering, opacity and brightness, and generally improve printing properties. The mineral fillers for papers are talc, hydrous kaolin, calcined kaolin, precipitated silica and silicates, and titanium dioxide.  The use of filler is important when opacity is needed at a low-basis weight. They are invaluable in packaging grades where low permeability is combined with opacity to protect food from light. Filler also decreases the energy demand in pulp and papermaking process due to lesser usage of fibrous mass . Loading of higher filler content in paper is always desirous by the papermaker due to decreasing cost and increasing optical properties.

The properties of filler are linked with the ability of the same to refract and backscatter light through the surface of the sheet.