Percoll is a tool for efficient density separation in Cell biology that was first formulated by Pertoft and colleagues.  It is used for the isolation of cells, organelles, and/or viruses by density centrifugation. Percoll consists of colloidal silica particles of 15–30 nm diameter (23% w/w in water) which have been coated with polyvinylpyrrolidone (PVP).
Percoll is well suited for density gradient experiments because it possesses a low viscosity compared to alternatives, a low osmolarity, and no toxicity towards cells and their constituents.
Percoll is a registered trademark of GE Healthcare.