Among the surprising properties that framework materials appear to exhibit more frequently than dense inorganic materials, "abnormal" mechnical properties are of key interest. Among those, we can list (far from being exhaustive): highly anisotropic elastic behavior, negative linear (or area) compressibility, negative Poisson's ratio, zero linear (or area) compressibility, pressure-induced softening, etc. Such properties, while not physically or thermodynamically forbidden, are considered relatively rare in crystalline materials in general, and their occurrence in some frameworks can qualify them as mechanical metamaterials. We present here some recent discoveries in this area of research, and refer readers to two book chapters for more complete reviews of earlier works, written by Arnaud Marmier and Sven M. J. Rogge. What is arguably the most eye-catching illustration of this direction of research is the recent report by Jin. et al of an "origamic" flexible MOF with folding-type molecular motions upon changes in temperature and the application of external pressure. In 2019, a previous work of the Choe group had already demonstrated the relevance at the atomistic level of the design principles of mechanical metamaterials usually applied at the macroscopic or microscale, through technologies such as 3D printing or micropatterning. More specifically, they showed that one could engineer a material with negative Poisson's ratio (a property also called auxeticity ) through the careful combination of (i) a Zn-based SBU serving as a hinge, (ii) a rigid porphyrin linker, whose only possible motion is a concerted rotation, and (iii) a framework topology compatible with auxeticity. The unusual mechanism of flexibility of this UPF-1 material is depicted in Figure . In 2023, Jin et al. extended this concept to another material, in a 2D framework inspired by the traditional Japanese craft of paper folding, origami (折り紙). The PPF-301 framework, 16 self-assembled from Zn nodes and flexible porphyrin linkers, is highly flexible and exhibits directions of exceptionnally negative linear compressibility and Poisson's ratio. This flexibility is associated with a concerted mechanism in the 2D sheets, which involves the folding of an origami-like tessellation, known as double corrugation surface (DCS), as illustrated on Figure . The concept appears to be generic, as the Choe group demonstrated in 2024 in Nam et al. by creating a new MOF named gis-ZIF-1 17 whose response under pressure and guest uptake demonstrates a similar mechanism, associated with a kirigami pattern (切り紙 is a variant of origami where paper cuts are allowed).