The energy absorption capability of an exposed crashworthy element or system is largely affected by material properties and structural design: prismatic sandwich structures, made of foam or honeycomb core between two metallic or laminated composite face plates, are good candidates. This work deals with a numerical investigation on the energy absorbing capability of such a structural component. There are several difficulties associated with the numerical simulation of a composite impact-absorber, such as high geometrical non-linearities, boundary contact conditions, failure criteria, material behaviour; that is because the main objectives of any numerical investigation are the calibration of the model with experimental results and the evaluation of the sensitivity of the variables with respect to the geometrical and physical parameters which influence the study at hand. The latter is a very relevant aspect for designers if the application of the model to real cases has to be a robust one from both a physical and a numerical point of view. In this paper a preliminary calibration of a numerical model for a composite impact absorber is presented, on the basis of experimental data found in literature; then a sensitivity analysis of the same model to the variation of the main geometrical and material parameters, developed by using the explicit finite element algorithms implemented in the Ls-Dyna code, is illustrated.