WG3 develops standardized, advanced, and non-destructive methods for characterizing the physicochemical and functional properties of fibers, ensuring consistency, reproducibility, and alignment with industry standards. By establishing harmonized protocols and conducting inter-laboratory studies, WG3 provides the scientific and quality-assurance foundation needed for evaluating bioactivity (WG4), supporting sustainability assessments (WG5), and enabling product development (WG6), ultimately facilitating regulatory approval and commercialization.