The insulated window construction is characterized in having a substantially uniform heat transition coefficient. The uniformity of the heat transition coefficient is obtained by increasing the distance between the window panes and the heat resistance in the edge region of the window is matched to that in the region of the window area which is undisturbed by the edge. The edge region is formed by a frame which has a pair of separate metallic frame members which are joined together and spaced apart by non-metallic webs so as to define an insulation path of at least 0.8 times the clearance between the panes.
