Flexo uses a flexible photopolymer relief plate. Ink is metered by an anilox roller — a ceramic roller engraved with cells of a controlled volume — transferred to the raised image on the plate, and then to the substrate under light pressure.
The anilox is what controls ink volume, and its specification (cells per inch and cell volume) is as important to the result as the ink itself.
Plate costs are far lower than gravure cylinders, making flexo economic for short and medium runs and for frequent design changes. Modern flexo quality is close to gravure for most packaging work.
Flexo inks are low viscosity and fast drying. Water-based flexo is well established in corrugated and paper applications; solvent-based systems remain common in film packaging, where adhesion and drying speed are harder to achieve with water.