  The Plateau-Rayleigh instability of a liquid column underlies a variety of
fascinating phenomena that can be observed in everyday life. In contrast to the
case of a free liquid cylinder, describing the evolution of a liquid layer on a
solid fibre requires consideration of the solid-liquid interface. In this
article, we revisit the Plateau-Rayleigh Instability of a liquid coating a
fibre by varying the hydrodynamic boundary condition at the fibre-liquid
interface, from no-slip to slip. While the wavelength is not sensitive to the
solid-liquid interface, we find that the growth rate of the undulations
strongly depends on the hydrodynamic boundary condition. The experiments are in
excellent agreement with a new thin film theory incorporating slip, thus
providing an original, quantitative and robust tool to measure slip lengths.
