Printing inks for digital production printing processes can be classified into two categories. Either the functional ingredient is dissolved in the carrier solvent on a molecular scale, or it is dispersed in the liquid to form of small particles, preferably nanosized. The latter is the case for most metal inks, the first for most functional polymers. Depending on the type of ink used, selecting either “closed” or a porous substrate surface can strongly influence the functionality and performance of the printed structures. It is shown, that for ink containing dissolved materials a “closed”, non-porous substrate surface is preferred, whereas for inks with particles a porous substrate with the right pore size may lead to surprisingly good results. For the ink-substrate interaction in the latter case a filtration mechanism is proposed, which leads to a removal of organic additives from the printed metal layer. This process enhances conductivity already in the uncured state, and facilitates fusing of the metal nanoparticles.