The development of 3D printing technology stimulates an active search for new methods of its application. Creating phantoms using a 3D printer is one of the promising areas. This will allow for more accurate and individual dosimetric monitoring during radiation therapy. The purpose of this work is to study the tissue equivalence of plastics used in 3D printing. The mass attenuation coefficient was determined based on chemical composition by calculation in the XCom database, which is presented and maintained by the National Institute of Standards and Technology (NIST). Then the linear attenuation factors were calculated. Linear attenuation coefficients were compared with 4 human tissues (liver, skin, kidney, and breast). Tissue attenuation values for photon radiation were obtained from International Commission on Radiation Units and Measurements report №44 (ICRU report №44). The average plastic / tissue ratio was calculated for the selected energy range (10–150 keV). Based on experimental data, it was found that PETG plastic is the best for imitating kidney and skin. This study shows that existing materials used in 3D printing can be used to create customized phantoms.