The acoustic analysis of the morphological evolution, from the surface to the bulk, of a vinylester resin cured in contact with two types of surfaces, i.e. aluminium and air, has been studied. The analysis was also performed as a function of styrene monomer content of the uncured resin. The existence of a thick layer, in which the vinylester network is deeply affected due to the relative variations of polystyrene and vinylester polymer from the interface to the bulk, was first demonstrated by microscopical Fourier transform-infrared spectroscopy. Secondly, this structural evolution was analysed by means of an acoustic scan technique, allowing the variations of the mechanical properties of the vinylester network to be estimated as a function of the distance from the interface. A good correlation was obtained between spectroscopic and acoustic results.