The optimal design of lightweight structures enables significant weight and energy savings, with applications spanning aerospace, automotive, and packaging industries. Weight reduction is typically achieved through thickness minimization and the use of architected or metamaterials, while preserving sufficient stiffness to maintain structural integrity under various static and dynamic load conditions. The complex responses of this type of structure reveal multiple solutions due to the buckling phenomenon and instabilities which are difficult to model with classical algorithms. This is also the case for other applications such as those involving soft materials that we can encounter in biomechanics or in the chemical industry. These soft components are capable of sustaining large deformations under diverse stimuli and often lead to complex responses involving multiple bifurcations. In this mini-symposium, we are interested in advanced experimental and numerical techniques developed for modelling the complex responses of soft materials and slender structures considering the interaction between different loading involved in mechanical systems. We hope to bring together experts working on these different aspects to review the emerging challenges and share the latest advancements in this research field. Topics of particular interest include but are not limited to : • geometric and material instabilities in soft materials • wrinkling, creasing, folding and ridging in extreme materials under various stimuli • shape buckling of flexural structures such as plates, shells and membranes • growth-induced deformations in biological tissues, biomaterials, bio-inspired structures • micro-structural and macroscopic modelling in composites across length scales • novel mathematical modelling method and constitutive theory