The objective of this paper is to investigate the effect of padding on the human thorax. Different types of padding are used in the computer simulations. Lumped models are developed to perform the simulations. Through the responses of the simulations one can determine what kind of padding is desired. This paper provides the first phase of using a computer-aided tool.Though much attention has been paid to either the investigation of padding or human thorax modelling, how the physical properties of padding affect thoracic protection is not well known. The combination of padding and the thorax needs a lot of effort to unveil their relationship. This paper attempts to provide the guideline of what a good padding material should be. The determination of an optimal padding is one of the goals in this study. Hopefully, the results of this paper can make a contribution to the vehicle safety design, especially the car door.A number of figures will be included in this paper to illustrate the responses of simulations. Numerical values of parameters of padding are also shown in this paper in the form of tables.In the lateral impact, the door structure and padding are the primary protection to the thorax. The former is not included in the scope of this study. The main emphasis of this paper is on the characteristics of padding. Because the padding acts as a bumper between the impactor and the thorax, the impact energy absorbed by the padding also indicates the performance of padding. As a result, the selection of a padding is made in order to reduce the remaining impact energy transmitting to the passenger. In this study injury scale is involved and AIS of less than 3 is chosen as the criterion.