The article presents research on multi-material 3D printing of samples composed of PLACTIVE (PLA-Cu) and TPU, manufactured using a 3D printer with a single print head equipped with a material station. The samples were produced in nine variants, differing in printing orientation (X, Y, Z) and the geometry of the material interface (flat, cubic, sine wave). The study aimed to perform a microscopic analysis of the quality of the interface between PLACTIVE and TPU depending on these variables. Structural observations of the joints were conducted to assess bond quality and identify potential defects in the transition zone. Additionally, microscopic observations of the samples after the tensile test were performed. The findings indicated that both the printing orientation and interface geometry significantly influenced the quality of the joint. Microscopic analysis allowed for the identification of weakly bonded areas and potential failure mechanisms, providing valuable insights for optimizing the multi-material printing process to achieve more durable composite structures.