Examples of glass filler (microspheres) and glass material (cut fibers) for plastics reinforcement: *glass microspheres (or glass beads); diameter: about 300 µm, specific gravity: 2.5. Mineral filler mainly used to increase the stiffness of a thermoset resin and to make road safety markings; *5 mm length chopped strands of fiberglass used to reinforce thermoset resins.