This investigation sets out to develop a more quantitative understanding of how paper structure impacts printing ink development. Two instrumental approaches are compared to monitor liquid penetration under: (i) capillary driven flow using an ultrasound method; and (ii) forced flow using liquid porometry. Commercial printing papers including xerographic, ink jet and newsprint grades, were evaluated using swelling (water) and non-swelling (polydimethylsiloxane) probe liquids. On the basis of these experimental studies the latest progress in developing a more realistic theoretical model to describe liquid penetration in paper and better quantify its behavior will be presented.