1)light grey,thin wall,hollow,light weight. 2)Volume weighs is 250 - 450kg /m3,granularity diameter is about 1 mm , Hollow glass micropheres is a hollow ball collected from coal powder,its coloure is light grey,thin wall,hollow,light weight.Volume weighs is 250----450kg /m3,granularity diameter is about 1 mm ,its surface is smooth and closed, and small heat conductivity, fire resistant rate ≥ ...