The structure of nylon-6 hybrids with synthetic or natural clays was investigated for melt-pressed films with Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and differential scanning calorimetry in comparison with the nylon-6 homopolymer. In contrast to the development of familiar alpha-form crystals in plain nylon-6 film, the hybrid films produced gamma-form crystals when nylon-6 was conjugated with synthetic mica, whereas the hybridization with natural montmorillonite gave rise to both alpha- and gamma-crystalline modifications. The degree of crystallinity of the nylon-6 hybrid with synthetic mica was the highest of the three series. Moisture sorption isotherms obtained for these nylon-6-based films were all typically sigmoid-shaped, although the prevalence of a higher crystallinity in the hybrid samples lowered the degree of moisture regain. The sorption behavior was analyzed well in terms of the parameters of a Brunauer-Emmett-Teller multiplayer adsorption model and a FloryHuggins treatment. It was also observed that the cluster formation of the water adsorbed into the nylon-6 matrix tended to be restricted by the hybridization with clay.