Flatfoot is a musculoskeletal deformity, particularly common in children. This condition can significantly impact the quality of life by causing foot pain, fatigue and musculoskeletal disorders. Typical clinical evaluations and standard methods offer valuable diagnostic insights, but they are often not suitable for capturing dynamic plantar pressure distributions during daily activities. To address this limitation, this work presents the development of a smart, 3D-printed Thermoplastic PolyUrethane insole, incorporating a flexible electronics layer with embedded load sensors strategically distributed across key plantar regions (rearfoot, midfoot, and metatarsal areas). This system enables real-time monitoring of plantar pressure using low-cost, flexible electronics, fabricated through rapid prototyping techniques. An experimental survey was performed to validate the system’s behavior and to characterize its main features. Transduction and calibration models have been obtained for each sensor, achieving a resolution in the order of 1.13 N and an uncertainty of ± 2.83 N in the worst case, in the 3σ level. Furthermore, a MATLAB®-based Graphical User Interface was developed to offer a real-time visualization of the plantar pressure map.