Several concurrent phenomena occur during the thermal inflation of poly(amic acid) precursor particles leading to polyimide foams as part of the solid-state powder foaming process. The precursor experiences bubble growth from within while volatiles desorb and the polymer itself increases its molecular weight and changes its backbone structure. These changes affect the transport properties of the material by modifying significantly the effective glass transition temperature, T-g. By studying the chemical transformations that take place during the inflation process (amidation and imidization reactions), a complete understanding of the material's molecular changes can be obtained and corresponding property changes can be followed. This article is the third of a series where the inflation of precursor materials for polyimide foams has been studied. The two previous articles in the series present numerical models that simulate the inflation process from first principles. In this article, the authors discuss the experimental and analytical methodologies employed to accurately characterize and incorporate the changes in material and transport properties as a function of the glass transition temperature.