This paper examines the use of Elastolit®SR* low-density Structural RIM (SRIM, Structural Reaction Injection Molding) systems applicable for interior trim door panel construction. Elastolit®SR low-density Structural RIM is a name encompassing CFC-blown, water-blown, and hybrid polyurethane systems. Composite reinforcements are discusssed. Typical mechanical properties derived from the use of water-blown systems are reported. Moreover, comparisons are made between low-density SRIM and more traditional materials of construction in terms of their mechanical properties and their concomitant manufacturing methods. Relative comparisons in manufacturing costs are presented. Lastly, the advantages of using low-density SRIM for door panels are fully summarized. One very important advantage discussed is vehicle mass reduction.