Knowledge of the behaviour of kinetic energy absorbers or impact attenuating devices is of paramount importance to design and research engineers involved in the automobile, aircraft, spacecraft, and nuclear industries. The main function of these devices is to minimise injury to personnel, to protect cargo that contain hazardous materials or to protect delicate structures from possible impact damage. Such industries require these devices to dissipate kinetic energy into an irreversible form and more importantly, in a controlled and desired manner. The performance of kinetic energy absorbers is significantly affected by various physical parameters such as material properties, mode of deformation and the nature of loading, with strain rate and inertial effects playing an important role due to high velocity impact. This work details the experimental and computational analysis of circular and oblong shaped kinetic energy absorbers subjected to quasi-static and dynamic lateral loading. The objective of this research was twofold; firstly, to design optimised kinetic energy absorbers which exhibit a desirable force-deflection response and secondly, to increase the specific energy absorbing capacity of such systems. The energy absorbers were in the form of a nested system consisting of a number of mild steel tubes of varying diameters assembled internally. The longitudinal axis of each tube was in parallel and an eccentric tube configuration was used. These systems were compressed laterally using three different devices: a flat platen, a cylindrical rod and a longitudinal line load indenter. It was found that the optimised designs for both the circular and oblong shaped devices exhibited very desirable features in terms of its force-deflection response. This was achieved by using a simple design modification which was incorporated into the optimised designs. Also, it was concluded that the specific energy absorption capacity of these nested systems can be increased notably by introducing external constraints which subject them to extra volumetric deformation. Both objectives were achieved using the finite element method, the results of which were validated using experimental techniques. It can be concluded that a new family of kinetic energy absorbers in the form of nested metallic systems have been designed which meet the objectives outlined and can thereby contribute to the literature in the field of kinetic energy absorbers.