Hollow glass microspheres are made from borosilicate glass.
These microspheres are hollow, but non porous.
True density of C-PHGL (Corpuscular Plain Hollow GLass) is size dependent;
11um, 18um and 30um hollow glass beads have true densities 1.1, 0.6 and 0.35g/cm3, respectively.
These microspheres are commonly used as a polymer additives and R&D
Hollow Nano Glass Beads : Size Range 10nm - 1000nm
