These products are designed for applications requiring monodisperse inorganic spheres. Like glass, silica has a much higher density than polystyrene and the opaque spheres provide more contrast than polymer particles in optical and electron beams. They are calibrated by NIST traceable methods developed by Thermo Scientific, and are suitable for a wide variety of particle measurement applications. They are packaged as aqueous suspensions in 15ml dropper-tipped bottles at a concentration of 2% solids. The silica spheres have a density of 1.8-2.2g/cm3 and an index of refraction of 1.40-1.46 @ 589nm (23°C).