In light of current environmental issues and the emerging context of bio-economy aimed at continuing economic growth while preserving the environment and earth resources, vegetal fibers are increasingly used to substitute glass fibers for polymer strengthening to make eco-composites. Indeed, the use of natural fibers allows bio-based and local resources to be valorized while lightening the overall weight and reducing the cost of composites. Flax fibers are usually considered as adequate bio-reinforcements for composites. However, their hydrophilic character makes them sensitive to moisture sorption and difficult to wet by hydrophobic resins. This incompatibility can induce a defective interface and micro-porosity between fibers and matrix that would greatly weaken the eco-composite’s mechanical performance[1][2][3] . Several ways have been explored to improve wettability of bio-based reinforcements towards resins. However, these techniques can damage the initial material and/or are generally harmful to the environment through the use of toxic products and solvents, which is against the idea of making environmental friendly eco- composites. It is in this context that fluorination treatment takes place. Indeed, a fast and controlled reaction treatment under molecular fluorine (F2 ) of wood[4] or vegetal fibers allows fluorine atoms to be covalently grafted on the outmost surface of lignocellulosic material in substitution of hydroxyl groups responsible for hydrophilicity. This grafting, achieved on flax fibers, allowed the fibers’ polarity to be significantly decreased without modification of their bulk’s mechanical performance. This reduce the gap between the surface energies of the fibers and different polymer matrix (bio-based epoxy and Elium®). In other words, the wetting of the fiber by the polymer is improved during the infusion process. Thereby, porosity into the composite thus formed is significantly reduced, increasing its mechanical performance, its health, and its life span during a humid environment aging, without any chemical coupling agent harmful to the environment [3][5] . [1] F. M. AL-Oqla, M. S. Salit, Materials Selection for Natural Fiber Composites, 2017, 23-48 [2] P.-J. Liotier, M.F. Pucci, A. Le Duigou, A. Kervoelen, J. Tirilló, F. Sarasini, S. Drapier, Compos. B. Eng. 163, 2019, 86–95. [3] M.F. Pucci, P.-J. Liotier, D. Seveno, C. Fuentes, A. Van Vuure, S. Drapier, Compos. A: Appl. Sci. Manuf. 97, 2017, 31–40. [4] M. Pouzet, M. Dubois, K. Charlet, A. Béakou, J.-M. Leban, M. Bada, 133, 2019, 133–141. [5] F. Saulnier, M. Dubois, K. Charlet, L. Frezet, A. Beakou, Carbohydr. Polym. 94, 2013, 642–646.