AbstractHighly crystalline polycaprolactam was prepared by zone polymerization of ε‐caprolactam. Folded‐chain crystallized and annealed, melt‐crystallized, and solution‐crystallized polycaprolactam was produced from commercial polycaprolactam. All samples were characterized by x‐ray diffraction, electron microscopy, density measurement, and heat of fusion measurement. The determination of the time‐dependent melting by DTA and scanning calorimetry revealed that all the different morphologies show different melting behavior. Zone‐polymerized polycaprolactam superheats, and the other morphologies reorganize on heating to different degrees. Densities and heat of fusion vary in the same manner—from highest to lowest—in the order: zone‐polymerized, solution‐crystallized, annealed, and melt‐crystallized. An estimate of heat of fusion, equilibrium melting point, and surface free energy was obtained