The alumina bubble produced by the company is a hollow spherulitic heat-insulating material, which is made by electro-fused method. It is noted for its light-weight, heat-resistance, and close pore. It is an ideal filler for high-temperature furnaces and excellent aggregate of light weight castable refractory. It is also and ideal heat-insulating and energy-saving refractory. The grain size is 0.2-1, 1-3mm, 3-5mm