Applied Microspheres Powder MicroStandard™ is designed for particle sizing and counting instruments that can only be calibrated using dry particles. They are available in the 3 to 220 μm range. Powder MicroStandard™ particles are composed of cross-linked polystyrene and have a density of 1,05 g/cm3 . The refractive index is 1,59 @ 589 nm. They are less suitable for redispersion in aqueous media.