One aspect of a method of manufacturing a honeycomb core includes positioning a first thermoplastic columnar cell adjacent a second thermoplastic columnar cell, modifying a thermoplastic property of the first thermoplastic columnar cell, wherein the modified thermoplastic property permits joining a circumferential surface of the first thermoplastic columnar cell to a circumferential surface of the second thermoplastic columnar cell. The method also includes joining the circumferential surface of the first thermoplastic columnar cell having the modified thermoplastic property to the circumferential surface of the second thermoplastic columnar cell resulting in the honeycomb core.