Other cell fillers used with glass microspheres
Hollow Glass Microspheres?Syntactic foams

Cenospheres are by-products recovered from the fly ash of pulverized coal-fired power plants.

The chemical composition of these fly ashes varies according to the origin of the coal used; they are essentially based on silica and alumina. These dark-colored cellular fillers have a density of 0.70 to 0.85 g/cm ³ , a particle size ranging from 10 to 300 µm and a compressive strength of around 15 MPa.