Silica opals are used as templates where CdS is infiltrated with the aim to build inverse structures with enhanced photonic band gap properties. A control on the degree of infiltration, from 0% to 100%, is attained. The band gap at L is studied finding that the width decreases and then recovers as a function of CdS infilling (from bare opal to fully loaded structure). This is well accounted for by theory based on two different modes for the growth of CdS inside the opal pores. A shell mode seems to govern the growth at low infiltration (less than 10%). High quality opal templates, appropriate sintering, and a high and uniform infiltration are required to ensure further optical characterization of the inverse systems. Only heavily loaded structures are apt to be inverted. The gap in the fully loaded and the inverse opal are, respectively, two and three times broader than in the starting opal.