In the three-dimensional bin packing problem the task is to orthogotnally pack a given set of rectangular items into a minimum number of three-dimensional rectangular bins. We give a characterization of the algorithm proposed by Martello et al. (2000) for the exact solution of the problem, showing that not all orthogonal packings can be generated by the proposed algorithm. the packings, however, have the property,of being robot, packings, which is relevant in practical settings. References to the modified algorithm, which solves the orthogonal as well as robot packable three-dimensional problem, are given.