This paper discusses the physical behaviour of “bending” waves in sandwich plates in which the facings are thin, stiff and heavy as compared with the core. By means of asymptotic expansions of the basic equations of linear elasticity, it is shown that different “physical mechanims” predominate in different frequency ranges. The consequence is that different, but relatively simple equations of motion may be used within limited frequency ranges. The predictions of such an equation, valid for moderate frequencies, are compared with measurements performed on glass-polyurethane sandwich plates. The agreement of theoretical and experimental dispersion curves for axisymmetric waves, and hence for plane waves as well, was found to be very satisfactory.