Printing quality is influenced by numerous parameters and by the material interactions in the ink- plate-substrate system. The aim of this paper is to characterize and quantify influential parameters in the flexographic reproduction system by using the method of the least squares (LS fitting). Specifically, this paper deals with influential properties of the printing plates and porous printing substrates (paper, board). Printing plate with its properties and interaction with the printing ink and substrate during the printing process affects the parameters of the print. Different properties of analysed porous substrates define properties of the print such as tonal values/dot gain and optical density. Measured properties of different printing substrates (papers and boards with different types of coatings) are used to build a quantification system of influencing parameters for the quality of the print using two different types of printing plates (patterned and non-patterned). Substrate parameters included in this research are roughness, surface free energy and gloss, while the surface free energy analysis was used to define printing plate properties. Results have shown that the least squares method can be applied to define the suitability of a particular type of printing plate for printing on different materials and enable optimization when selecting the material parameters in the flexographic reproduction system.