<p>Additive manufacturing, particularly 3D printing using fused filament fabrication (FFF), has enabled the fabrication of complex parts by combining different materials in a single process. However, when combining rigid and flexible polymers, such as polylactic acid (PLA) and thermoplastic polyurethane (TPU), the mechanical behavior of the resulting bimaterial parts depends heavily on the configuration and interaction between the materials. This study investigates how the geometrical arrangement or disposition of TPU within PLA structures affects the tensile mechanical properties of 3D-printed bimaterial specimens. Two configurations were tested: (1) superimposed layers of PLA and TPU, and (2) TPU sandwiched between PLA shells. In both cases, specimens were printed with varying TPU content (10% to 50%). Tensile tests were conducted, and the PLA/TPU interface was mechanically characterized using a single-lap joint model. A video extensometer was employed for accurate strain measurements. The results revealed that the interface stiffness was relatively low (64 MPa), contributing to premature failure in some configurations. In the layered configuration, increasing TPU content from 10% to 50% caused a 36% decrease in stiffness and a 58% reduction in tensile strength. In contrast, the sandwich configuration improved flexibility by ~ 25% and maintained higher stiffness (modulus of 1190 MPa versus 1021 MPa in the layered structure), indicating superior load transfer and strain distribution due to symmetrical TPU placement.</p>