Glass microspheres (hollow glass microspheres, sometimes termed microballoons, or glass bubbles) are microscopic spheres of glass manufactured for a wide variety of uses in research, medicine, consumer goods and various industries. Glass microspheres are between 15 to 120 micrometers in diameter.
Hollow spheres are used as a lightweight filler in composite materials such as syntactic foam and lightweight concrete. Microballoons give syntactic foam its light weight, low thermal conductivity, and a resistance to compressive stress that far exceeds that of other foams.These properties are exploited in the hulls of submersibles and deep-sea oil drilling equipment, where other types of foam would implode. Hollow spheres of other materials create syntactic foams with different properties, for example ceramic balloons can make a light syntactic aluminium foam.
Hollow spheres also have uses ranging from storage and slow release of pharmaceuticals and radioactive tracers to research in controlled storage and release of hydrogen. Microspheres are also used in composites to fill polymer resins for specific characteristics such as weight, sandability and sealing surfaces. When making surfboards for example, shapers seal the EPS foam blanks with epoxy and microballoons to create an impermeable and easily sanded surface upon which fiberglass laminates are applied.