In this paper, an efficient optimum material design technique is introduced for hybrid designing of dual-phase heat-resisting functionally graded composites. The graded region is divided into a finite number of homogeneous material layers in order to reduce the total design variables. The discrete optimum volume fractions are sought by making use of the interior penalty method and the finite difference sensitivity scheme. A linear interpolation technique is adopted to make the final optimum volume fraction distribution be continuous. The validity of the proposed optimization technique is examined through the illustrative numerical experiment.