Microsphere refers to a spherical microparticle between 1 and 1,000 microns (μm) in diameter (see Figure 1). Also known as spheres, balls, beads or micro-balloons, microspheres are manufactured from a variety of raw materials. The most common types are solid and hollow glass or polymer microspheres, as well as ceramic. Each type is designed in different grades depending on the application and quality requirements. The quality of the microspheres ranges from monodispersed microspheres produced under tight specifications, to microsphere grades with variations in particle size and sphere uniformity.