Abstract: A system and composition is disclosed for binding rocket motor propellants directly to the insulation layer within the rocket motor. Conventionally, it is necessary to place a liner layer between the insulation and the propellant. The present invention is particularly adaptable for use with hydroxy-terminated polybutadiene-type (HTPB) propellants. The method of the invention involves coating the insulation layer with a reactive material, such as a solution of isophorone diisocyanate (IPDI). The reactive material is then allowed to penetrate the insulation layer. Once sufficient penetration is achieved, the HTPB-based propellant is applied over the insulation layer to form a rocket motor propellant grain. The IPDI reacts with both the insulation layer and the propellant and forms a strong bond between the two. In the case of the propellant, additional urethane linkages are generally formed, which results in an area near the bond which may be harder than the propellant grain as a whole.