Adhesional characteristics of an elastomeric liner composition toward a highly filled composite matrix and metal case were investigated. The system is composed of an excess isocyanate functionality in the elastomer compared to an excess hydroxyl functionality in the composite matrix. Both phases essentially contain the same binder (HTPB) and curing agent (IPDI). A bifunctional aziridine (MAPO) is used as a bond (adhesion) promoter. The effects of the R value, triol/diol ratio, and MAPO concentration on the adhesive nature of the metal-elastomer-matrix system were investigated by tensile and peel test methods. Maximum T-peel values were obtained for the NCO/OH ratio of R = 1.15 and for the triol/diol ratio of 0.054. The optimum MAPO concentration was found to be around 1-2% for the elastomer. As a result of this investigation, three candidate compositions were selected to be employed as an elastomeric material. On these compositions, metal-elastomer-composite (MEC) tensile, MEC-shear, lap-shear, elastomer-composite (EC) peel, and T-peel tests were applied. These compositions reflect acceptable combinations of strength and elasticity as well as good adhesive values required for a liner material. In particular, one of the compositions tested seems to be a good candidate when all the required characteristics of an elastomeric liner material are considered. It has a large enough elasticity with the required modulus to withstand the compressive and shearing forces in applications together with good adhesive properties toward the composite matrix and the metal.