Growing concern about resource consumption in the construction industry has brought new challenges to the design of façades. Compared to traditional techniques, AM stands out for the possibility of fabricating complex geometries embedding multiple functions. This study explored how the potentials of Fused Deposition Modelling can be used to create a multi-functional façade element for thermal insulation and structural stiffness. Physical testing and software simulations have been performed to assess the properties of complex geometries and retrieve design guidelines. A digital workflow was developed, encompassing performance-driven design, performance assessment and geometry generation for fabrication. The study highlights how, by manipulating porosity and material distribution, it is possible to design stiff, insulating envelope components which are suitable for manufacturing with FDM using polymers.