Cenosphere(floating bead) is a kind of fly ash hollow ball which can float on the water surface. It is gray white, thin and hollow with light weight. Its volume weight is 720kg / m3 (heavy weight), 418.8kg/m3 (light weight), particle size is about 0.1mm, its surface is closed and smooth, its thermal conductivity is small, and its fire resistance is ≥ 1610 ℃. It is a good temperature keeping refractory material, widely used in the production of light castables and oil drilling.