Specification 75, 160, 106, 300, 500..... and so on Density: (g/cc) < 0.90 g/cc Sinker: (%) < 10% Moisture: (%) < 1%... Cenospheres are hollow ceramic microspheres found in flyash, a natural by-product of coal combustion during the generation of electric power. Small and hollow, microspheres are used as functional fillers or extender in the manufacture of plastics, paints,resins, thermal coatings ...