The development of rapid prototyping technologies generates a strong concern for saving all types of materials while maintaining, or even increasing, the strength of 3d printed parts. One way to partially meet this requirement is to make models with a low degree of filling. However, the types of predefined filling structures, defined in the slicing programs, are relatively small in number, being based on repetitive patterns. In this paper it is proposed to make a specimen with a filling

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... e adapted to the expected stress that appear during operation. Model design can be done in any computer-aided design environment. The deformations of the modified specimen were compared with the deformations of some models with predefined filling structures, under the conditions of maintaining the same loads. This comparison allows to verify the strength of the specimen, under the conditions of using the same volume of material, compared to the models with predefined structure. In addition, conclusions can be drawn regarding the strength of various filling patterns and the time required to print the specimen. The favorable results create the premises of developing an algorithm that can allow the generation of some filling models optimized for different types of loads and eventually the possibility of applying the same concept of custom filling structure for other rapid prototyping technologies.