3M™ Glass Bubbles are made of low alkali borosilicate glass, thus they can be processed with cements. The average volume is approximately 8 liters/kg. This makes the hollow glass beads very inexpensive to use. Already with 125 g of hollow glass beads to one liter of mortar, the specific weight of the mortar mixture by about half. Hollow glass beads are quite excellent thermal insulators. Although hollow glass beads are very stable, they should never be used with roller mills or dispersing machines.