The lamellar orientation domains were color-coded based on their orientation (using the Directionality plugin of Fiji ) to facilitate the identification of their boundaries. Once the crack is initiated at the tip of the notch, it propagates in different directions depending on the orientation of the domains it encounters, along the boundaries of the orientation domain. This propagation path is intradomain when the pores in the domain are favorably oriented. A strong change in crack direction is observed at the domain boundary (A marks in Fig. ). Because of the presence of orientation domains, there is not a single weak direction in the material. This behavior increases the crack tortuosity. These results are in good agreement with the role of orientation domains identified by Lichtner et al. in 1D compression tests. This extrinsic mechanism, coupled with the crack bridging provided by the PCL, adds an additional toughening mechanism to the material.