The cell nucleus is surrounded by a spherical double membrane called the nuclear envelope. Scientists have long been intrigued by how this envelope can be elastic enough to accommodate shape changes that cells experience as they move through tissues, but also rigid enough to maintain nuclear integrity. A study by Anete Romanauska and Alwin Köhler, published in Nature Cell Biology, uncovers that the chemistry of membrane lipids is key for this versatility. When this chemistry is perturbed, the nuclear membranes become stiff and prone to rupture, and nuclei lose their typical round shape and morph into a polyhedron.