A Systematic Review of 3D‐Printed Flexible Strain Sensors: Materials, Architectures, and Performance

3D‐printed flexible strain sensors are attracting increasing interest in wearable health monitoring, soft robotics, and broader mechanical sensing because 3D‐printing enables compliant, geometry‐controlled, and increasingly integrated sensor architectures. This systematic review, conducted in accordance with PRISMA 2020, examines 76 peer‐reviewed experimental studies published between February 2014 and March 2026 on 3D‐printed flexible strain sensors. The analysis compares 3D‐printing routes, conductive material systems, transduction mechanisms, application domains, gauge‐factor reporting modes, strain‐range reporting, and durability‐related performance metrics. A key contribution of this review is the traceable separation of linear and maximum gauge factor reporting, together with the distinction between linear operating range and absolute strain capacity. Material extrusion emerged as the dominant manufacturing approach and was most strongly associated with carbon‐based conductive elastomer composites, whereas direct ink writing and vat photopolymerization were more widely implemented for ionic, hydrogel, and ionogel‐based systems. Around 20% of studies reported linear gauge factor, whereas more than 50% reported maximum gauge factor; similarly, absolute strain capacity was extractable in more than 60% of studies, but clearly defined linear operating ranges were reported far less consistently. Overall, 3D printing should be regarded as a design framework for co‐optimizing material, structure, and sensing function.