This study explores how atmospheric-pressure plasma treatments can modify the surface properties of polyamide 6 (PA6) and its nanocomposites reinforced with organomodified montmorillonite (OMMT), materials developed as potential liners for Type IV composite overwrapped pressure vessels (COPVs) designed for hydrogen storage. Four material compositions were examined: neat PA6 and composites containing 1, 2.5, 5, and 10 wt.% OMMT. Two different plasma systems—a piezoelectric plasma brush and a rotary plasma source—were used to activate the surfaces, and their effects were evaluated using water contact angle (WCA) measurements and Fourier transform infrared spectroscopy (FTIR). Both plasma treatments effectively increased the wettability of the tested materials, but the rotary plasma consistently produced the lowest WCA values across all compositions, reaching as low as 21° for neat PA6. These findings suggest that the rotary plasma’s higher power and dynamic exposure enhance the formation of polar functional groups and may increase micro-scale roughness, leading to improved surface activation. FTIR results confirmed the appearance and growth of oxidized functional groups, particularly carbonyl and hydroxyl species, which are linked to the increased surface polarity and hydrophilicity. Time-dependent contact angle tests revealed that the effects of plasma treatment were not permanent. Over several hours, the contact angles gradually increased, returning close to untreated values.