This study introduces Structure-Property-Function (SPF) relations as a means to align rapid material development with technical system design. By systematically associating material structures with desired functions through property calculations, SPF relations optimize material performance for specific applications. We demonstrate this methodology by examining the hierarchical functions of Glass Fiber Reinforced Plastic (GFRP) specimens with integrated filaments as sensors. First, we present SPF relations for carbon nanotube (CNT)-doped filaments. Tensile testing extracts key mechanical and piezoresistive properties, which are linked to structural and strain sensing functions to identify optimal candidates for integration into GFRP specimens. At the composite level, we analyze GFRP specimens embedded with these filaments, connecting structural configurations, material properties and functional performance. We explore various GFRP structures based on filament placement and treatment methods. Subsequently, GFRP performance is validated through three-point bending tests, revealing insights into the structural and strain sensing capabilities of the composite material. Results emphasize the nonintrusive integration of filaments into the laminate and highlight the impact of surface treatments on piezoresistive behavior. In conclusion, SPF relations offer a novel approach to accelerate and enhance composite material system design, broadening material applicability and advancing the development of customized composite solutions.