The interior of nuclear pore complexes (NPCs) is densely filled with FG-nucleoporins that form a permeability barrier of a still-obscure nature. Celetti et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201907157 ) now reveal that FG-nucleoporins can undergo liquid–liquid phase separation and form liquid droplets that mimic permeability barrier properties of intact NPCs.