Two organically modified (Cloisite® 30B and 10A) and one unmodified clay (Cloisite® Na) were added to a resol‐type phenolic prepolymer. The modified montmorillonites showed a better dispersion in the prepolymer. The dispersion of the clay, the chemical structure as well as the thermal degradation behavior of the cured polymer and nanocomposites were studied. It was observed that the addition of Cloisite® Na leads to enhanced crosslinking of the cured polymer, leading to a higher activation energy for thermal degradation. The resol with Cloisite® 10A contained a higher percentage of voids, which seems to be one of the major factors that reduce hardness and adhesive strength when the nanocomposite was applied to a metal substrate.magnified image