The transition behavior and thermal properties of nylon-6 at elevated pressure, p, have been established by in-situ thermal conductivity kappa, and heat capacity measurements The glass transition temperature, T-g of virgin nylon-6 is described well by the empirical equation T-g(p) = 319 60(1 + 1 90 p)(0 24) (p in GPa and T-g, in K) Moreover isobaric heating in the 1-1 2 GPa range causes a cold crystallization transition near 500 K As a result, K increased similar to 15% whereas the heat capacity per unit volume decreased similar to 7% slowly with time during 4 h annealing at similar to 530 K The transformation is associated with a significantly increased crystallinity, from similar to 35% to 55-60%, and a pressure-induced preferred orientation and increased size for the lamellae of monoclinic a crystalline structure This state has 8-10 K higher melting temperature and better formic acid resistance than that of virgin nylon-6 However, the results show no indication of cross linking, as reported for similarly treated nylon 1010 and nylon-11, but instead chain scissoring