High repair cost and the subsequent increase in insurance cost in a highly competitive automobile market have forced every automobile original equipment manufacturer (OEM) to comply with the FMVSS and ECE-42 regulatory requirements of low-speed vehicle damageability. Although, the terminologies used are different, similar regulatory requirements also exist in Asia-pacific region. At the rear side, reducing the damage to expensive vehicle components in a low-speed pendulum impact or a low-speed barrier impact can attain a good rating for low-speed vehicle damageability. This paper focuses on a detailed study of various lightweight plastic rear beam designs and their effectiveness in reducing the damage to the vehicle during low-speed vehicle-to-vehicle collision or vehicle to barrier collision.Six parameters namely, vehicle mass, reaction force levels, vehicle width or the distance between the rails, intrusion levels, beam height and beam mass (or thickness) are taken as the parameters for comparison. These parameters are computed for three to four types of plastic beams and the most effective beam design, for a given vehicle, with the optimum mass and the optimum performances measures are derived out. The study also compiles the minimum intrusion levels that can be achieved for a given beam mass, given beam geometry for a given vehicle. Finally, an informative matrix is developed, that helps to quickly identify the optimal beam geometry and its dimensions for given vehicle parameters.