Septins are cytoskeletal scaffolding proteins that directly interact with the inner plasma membrane to influence membrane remodelling. In humans, 13 different septins contribute to hexameric or octameric complexes. Diverse combinations of septin hetero-oligomer composition can confer differing structural and functional properties, but the number of possibilities makes examining intrinsic properties of septin filaments in vivo extremely complicated. Using cell-free in vitro and computational approaches, Aurélie Bertin and colleagues (Nakazawa et al., 2023) study how controlled, purified septin octamers behave on lipid surfaces with varying properties. They first show that septin organizes differently on convex versus concave membranes with micrometre-scale curvature, assembling perpendicular to ‘valleys’ and parallel to ‘hills’. Above a threshold concentration, septin forms a second layer of filaments orthogonal to the first, creating a mesh-like structure. Moreover, purified septin not only preferentially localises to curved regions of lipid vesicle membranes, but also induces uniform micrometric convex membrane deformations. Based on a computational simulation of the septin network modelled as a two-dimensional liquid crystal on a fluid membrane, the authors suggest that this effect likely arises from protein-membrane and protein-protein interactions between the first and second filament layers. Taken together, these sophisticated reconstitution studies provide new insight into fundamental properties of human septins.