Although the same fibers were used, different fiber impregnation mechanisms and different fiber-matrix interface properties are suspected to be at the root of these different trends in mechanical properties, as suggested by comparing the fracture surface of PLA/Flax-paper in Fig. 7 with that obtained in [8] where in presence of paper, the fracture surface was confined at a specific location along the coupon with a fracture surface almost perpendicular to the load direction. A more detailed investigation is discussed in the section ‘‘impregnation behavior”.