The first examples of covalent organic frameworks (COFs) were discovered in 2005, but quality has been poor and preparation methods uncontrolled. Now researchers have produced high-quality versions of these materials, demonstrate their superior properties and control their growth. The team’s two-step process produces organic polymers with crystalline, two-dimensional structures. The precision of the material’s structure and the empty space its hexagonal pores provide will allow scientists to design new materials with desirable properties.