AbstractThe damping properties of surface phonon‐polaritons, especially long‐range surface phonon‐polaritons in bilayer systems are analysed. An analytic expression is derived for the damping function by means of a perturbative method. The different behaviour of the damping properties of surface phonon‐polaritons for various physically different bilayer systems are discussed. It is shown that not all possible cases yield long‐range surface phonon‐polaritons. In some cases one or two modes show the behaviour of long‐range surface phonon‐polaritons. In special cases, there two longe‐range surface phonon‐polariton modes exist, one of these shows in a small frequency range a significantly increased propagation length. The propagation properties are analyzed numerically in dependence of frequency and of the thicknesses of the two layers of the bilayer system. Dispersion curves, the electromagnetic fields, the energy flow, the power flow, and the propagation length of the surface phonon‐polaritons are given in graphic