Filler. Coloured scanning electron micrograph (SEM) of Sillitin Z 86 by Hoffmann Mineral, an active filler composed of corpuscular quartz and lamellar kaolinite. A filler is a relatively inert material added to a basic resin or adhesive to alter its physical, mechanical, thermal or electrical properties, or to reduce cost. It has the appearance of a free-flowing light-coloured powder and can be used on its own or in combination with other fillers. Applications include pharmaceutical rubber goods, cable coverings and insulation. Magnification: x8300 when printed 10 centimetres wide.