Abstract ElectroInk, developed and manufactured by HP Indigo Division for its digital printing presses, is a complex fluid of unique rheological and electrical properties. Depending on the shear and the electric field the ink may be solid- or fluidlike. As ElectroInk propagates in the press from the ink reservoir to the substrate, the concentration increases while the structure of the ink changes from a dispersion of non-interacting particles to an elastic solid. The authors’ model treats ElectroInk as an interwoven structure of two continuous phases, one being a network of pigmented resin particles and the other the incorporated liquid. In an external electric field the network shrinks like a sponge and partial phase separation occurs. Application of the model is shown for the design of 100% transfer of ink from roller to roller in the press, which is necessary to meet the principal requirement of digital printing, that each printed page can be different.