Building self-assembled ‘molecular straws’ from bis-urea macrocycles, a research team has developed a new nanotube system that can be used to directly compare single-file diffusion dynamics with Fickian diffusion dynamics. The team uses hyperpolarized xenon-129 NMR to study gas transport dynamics in two highly homogeneous nanotubes, one with a narrow-bore, hollow interior that can accommodate xenon gas atoms only in single file.