A systematic parameters study is performed in a DC pulsed glow discharge in nitrogen in order to improve the wettability of thin polystyrene layers. The experimental parameters considered are the pressure P, the interelectrode voltage V, the frequency ν of the pulsed power supply and the treatment time tt. The wettability is characterized by the contact angle technic. The $(\Theta_{\rm i} - \Theta_{\rm f})/\Theta_{\rm i} = \Delta \Theta / \Theta_{\rm i}$ ratio is measured, where $\Theta_{\rm i}$ and $\Theta_{\rm f}$ are respectively the initial and final contact angles. In the first part of the paper, the variations of $\Delta \Theta / \Theta_{\rm i}$ as a function of the electrical energy E are investigated, the variations of E being obtained by modifying the parameters V, ν and/or tt. In the second part, the specific energy ε and the economical criterion γ are introduced to deduce the best running conditions through a chemical engineering approach. Taking into account the weak duty factor of the power supply (1% ), it is shown that the polymer surface is treated with a minimum of energy.