Negative Poisson’s ratio (NPR), also known as “auxetic”, is a phenomenon associated with a material that experiences transverse expansion when a tensile load is applied in the longitudinal direction. On the other hand, if the material is under a compressive load, it contracts transversely. The NPR materials are a novel class of materials, which have advantages that conventional materials may not possess [
22]. Materials with NPR have triggered significant interest in the scientific community because of their unique physical properties [
23–
27] including high shear modulus, high indentation resistance [
28], large plane strain fracture toughness [
29], and excellent shock and sound absorption abilities [
30,
31], and all of which are highly desirable properties for engineering applications. Specifically, the NPR materials can be used in microelectromechanical systems (MEMS) and fastening devices due to their auxetic characteristics, and they can be also added into engineering structures (e.g., sandwich or laminated panels in the aerospace industry) as energy absorption components. The natural materials found with NPR are polymers with microporous characteristics. Such polymer consists of a randomly or periodically distributed 3D array of particles interconnected by fibrils in the microscopic scale. For instance, microporous polytetrafluoroethylene (PTFE) film has a network of individual fibrils which can be extended by several microns in both directions when under uniaxial tension [
32,
33]. On the other hand, auxetic materials could be achieved via designing and tailoring their microscopic compositions and structures. Such man-made materials consist of a large number of unit cells, which are arranged into certain periodical truss patterns such as reentrant type, chiral type, or rotating units [
32]. Recently, it has been reported that laminated composites reinforced with microfibers can gain out-of-plane NPR [
34] through design and optimization of stacking sequences. However, there are still some limitations in engineering applications for the above NPR materials. For example, the majority of materials fabricated only have NPR in certain directions where the stiffness is low in those directions. Hence, such materials may only be used as the core for sandwiches which need to be enhanced by composite face sheets. In addition, NPR is usually achieved in the out-of-plane direction of a structural element rather than in the in-plane direction [
35–
37]. The research on composites with in-plane NPR is still in the conceptual stage [
38,
39] due to the unavailability of such type of NPR materials and their associated material properties for structural applications. Nevertheless, as hinted in the literature [
40], there is a possible approach to obtain in-plane auxetic composites by using the matrix and the reinforcing phase that both possess the in-plane auxetic property.