Crystalline slip has been observed in singly and doubly oriented nylon 66 and 610 by deformation of bristles in compression parallel to their orientation direction to form kink bands. The angles of the bands correspond to two and three (010) planes acting in unison as lamella in the kinking process. Slip was also manifested along a unique crystallographic plane (010) and a unique crystallographic direction ([1,3,14] and [1,3,18] in nylon 66 and 610) during fracture experiments on doubly oriented bristles. To account for this behavior a model of the structure of these oriented polymers is proposed in which the material is considered essentially completely crystalline with many vacancies and dislocations within the lattice. The dislocations and their motions which account for the observed deformations are illustrated. The difference between observed values of density and the theoretical density of nylon 66 is attributed to vacancies. The so‐called amorphous background in x‐ray diffraction patterns of these nylons is attributed to the vacancies and dislocations in the crystal structure.