Polystyrene Latex Beads are PSL Spheres for use in calibration of a size response curve using NIST traceable, size standards with narrow standard deviation of the size peak. The mean size diameter of these PSL spheres are calibrated with NIST traceable microscopy methods. The size distribution and uniformity are measured by electrical resistance analysis or optical microscopy. Polystyrene latex spheres range from 1 µm to 160 µm and are made from polystyrene (PSL). PSL Spheres are used instead of irregularly shaped particles to minimize the laser response of analytical instruments that are sensitive to particle shape. Products from 1 to 160 µm are packaged as aqueous suspensions in 15 mL dropper-tipped bottles. Concentration is maintained at 1.05 grams per cm cubed. Each bottle of PSL spheres contains a Certificate of Calibration and Traceability to NIST which includes a description of the calibration method and its uncertainty, and a table of chemical and physical properties. Packages are lot-numbered for convenient technical service and support after the sale.