The paper proposes a conceptually new method for thermal insulation system optimization. The method, based on minimizing thermodynamic irreversibility, consists of externally controlling the variation of heat leak with temperature across the insulation. It is demonstrated that the useful power savings registered from applying this design philosophy are important. Prime candidates for this method are insulation systems facing high absolute temperature ratios and insulation systems in which the effective thermal conductivity increases with the absolute temperature. Three classes of thermal insulation systems are optimized based on this universal design procedure: one-dimensional continuous insulations, insulations with discontinuous temperature distribution and continuous insulations with internal heat generation. © 1979.