Researchers from the Fritz-Haber Institute of the Max-Planck Society in Berlin identified aluminum monofluoride (AlF) as an excellent molecule to be laser-cooled to ultra-low temperatures with a high density. Atoms have been laser-cooled with great success for over 30 years. Recently, this powerful technique has been extended to small molecules, but a major challenge remains: to increase the density of the laser-cooled molecular gas by many orders of magnitude. AlF has the potential to achieve this, and recent developments in laser technology now make it possible to use this molecule. AlF is stable and deeply-bound with unique properties, enabling cooling to very low temperatures and with a high density.