The impedance presented to the inside surface of a hollow, liquid filled, radial cylinder of finite length has been determined theoretically. It was assumed that the liquid was retained by pressure‐release caps or one pressure‐release cap and one rigid cap at each end. For a loss‐free liquid it is shown that the reactance presented to the cylinder wall becomes infinite whenever the liquid has a longitudinal or coupled radial resonance.A sizeable resistance may appear when a viscous liquid is used. This is because the geometry of the arrangement is ideal for creating large shear losses. Exceptions to this occur for high frequencies where the wavelength is small in comparison to the cylinder length.