Researchers at the University of Twente and Utrecht University have packed rigid, rod-shaped particles into soft lipid containers the size of a living cell and watched the container and its contents reshape each other. The vesicle’s form determines how the rods line up; the tightly packed rods, in turn, bend the container into new shapes. This provides a minimal model for how physical coupling between a soft boundary and internal filaments can help cellular structures organize from within. The paper is published in the Proceedings of the National Academy of Sciences.