Sol-gel-based zirconia (ZrO2) and silica (SiO2) were obtained in situ via hydrolysis-polycondensation of metal alkoxide precursors in membranes of poly(3-hydroxybutyrate) (PHB). What followed was an assessment of thermal and spectroscopic effects from the insertion of the inorganic network in the PHB matrix. The findings exhibited a dependence of both the concentration and the chemical nature of the precursor on the properties of the as-formed inorganic-organic hybrids. The results also indicated that positive nucleating effects, a reduction of the crystallite size and a variation in thermal transitions correlate with spectroscopic data from the alpha and beta crystal forms of the PHB matrix, as well as the crystallization data obtained through polarized light microscopy. POLYM. ENG. SCI., 2020. (c) 2020 Society of Plastics Engineers