Bent-core mesogenic molecules organize into layered smectic liquid-crystal phases that have a strong inherent tendency for saddle-splay deformation of the molecular layers. One important class of such materials are the helical nanofilament phases, hierarchical self-assemblies in which growth of the liquid crystal is limited to twisted filaments that have saddle-splayed layers exhibiting Gaussian curvature but no net curvature (insets). These filaments pack to fill space in the bulk phase, but at the liquid-crystal–glass interface they exhibit a variety of exotic intermediate focal conic-related structures (background) having both Gaussian and net curvature, formed from the competition between the surface constraints and the tendency for layer twist. The work is presented by D. Chen, N. A. Clark et al. on p. 155 Ms. Heulwen Price is kindly acknowledged for putting the finishing touches to the cover image.