Prostheses and orthoses are trending towards digital methods and automation. Adopting these methods is especially a challenge at Frank Jol, a clinic where patients' wide variety in residual limb characteristics and high activity demands pose a challenge for digital workflows which utilise 3D scanning to arrive at a final prosthesis. This is because certified prosthetists and orthotists (CPOs) who design and produce prostheses, apply a series of tactile adjustments to the residual limb using plaster that result in a more optimal fitting and distribution of weight in the socket, which cannot easily be captured and digitised. In collaboration with Gyromotics, a high-tech prosthetic foot start-up, and Frank Jol, this graduation project is an exploration into the potential for a pressure-sensing textile tool to capture the tacit knowledge of CPOs in the fitting of below-knee prostheses. The project begins with a detailed analysis. First, the clinical situation of the residual limb and the biomechanics of transtibial prosthesis is studied to understand what factors influence prosthesis fit, and how CPOs manipulate the residual limb to that effect. Then the process towards producing a prosthesis is analysed as it is executed at Frank Jol, in order to then compare to alternative processes that incorporate digital methods to understand the barriers and opportunities for intervention. Finally, CPOs and patients are interviewed to uncover their needs and values in the process. This analysis reveals the need for an intervention that captures and standardises the stump modification process in a digital way, while retaining CPO control and tactiliy, and keeping the patient in the communication loop. The design result is PressFit: a pressure-sensing textile tool to be worn by the patient, which registers CPO applied pressures and provides visual feedback during stump measuring and plastering. PressFit is introduced as it fits into an envisioned future prosthesis prescription workflow. PressFit is developed through iterative technical development of the physical prototype, alongside development of the interaction for both measuring and plastering use cases. A co-design method with a CPO is followed throughout this development. An evaluation is conducted with 5 CPOs at Frank Jol to assess the prototype's performance against design drivers. Results show that PressFit standardises the measurement process. All participants agreed PressFit is a helpful tool with potential to improve patient-CPO communication and bring traceability to the plastering process. Additionally, the tool shows promise for us as a training tool for new CPOs. As this thesis serves as a proof-of-concept for the application of pressure-sensing textile in the prosthesis prescription process, it concludes with recommendations for further development in physical prototyping (textiles), software, and user interaction.