Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the alpha-phase, the addition of clay silicate layers favor the formation of the gamma-crystalline phase in PA6CN. We focus on the reason why silicate layers favor the formation of gamma-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the gamma-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding. The silicate layers were indeed found to weaken the hydrogen bonding both in the alpha- and gamma-phases This was also confirmed by X-ray diffraction studies. The gamma-phase is most likely concentrated in regions close to the silicate layers, whereas the alpha-phase is favored in the bulk matrix.