Hollow Glass Beads(Microsphere) Hollow glass microsphere is a light weight, inert, hollow sphere comprised largely of silica and alumina and filled with inert air or gas. Hollow glass microsphere is made from Soda lime borosilicate glass. They are produced at the high temperature of 700-800 degrees Celsius through complicated chemical and physical transformation. The color of Hollow glass microsphere is white and the specific gravity of them is about 0.05-0.50g/cm3, which gives them a great buoyancy. Hollow glass microsphere are hard and rigid, light, waterproof, innoxious, and insulative.