In this talk I will present an improvement of the approach to the Steiner problem proposed by Amato, Bellettini and Paolini, which is based on the minimization of the perimeter of subsets of a suitably chosen covering space. In this setting I will define a proper notion of calibration giving some examples. Finally I will focus on a calibration argument that allows to prove the minimality of the Steiner configurations for the vertexes of a regular hexagon. This is a jointwork with Alessandra Pluda.