Solid rocket motors typically include an outer case or shell that houses solid propellant grains. Internal insulation in a solid rocket motor is a layer of heat-barrier material placed between the internal surface of the case and the propellant which. The aim of the present study is to develop and characterize an asbestos-free rubber for use as rocket motor insulator which needs to be taken into account for protecting in the planning of space missions, in their design, and in their operation. Such insulation is based on aramid fiber in the pulp form, alumina and/or silica aerosol as reinforcement for Ethylene Propylene Diene Monomer (EPDM). Different formulations based on these fillers were prepared. The fillers dispersed in the EPDM polymeric matrix to obtain a homogenous master batch for curing. The physical, mechanical (density, hardness, tensile strength and elongation) and thermal properties (effective thermal conductivity) of different compositions were obtained. The ablation resistance of samples with different compositions was measured. Thermo-gravimetric analyses versus reinforcement content were obtained. The effect of changing aramid fiber in the pulp form, alumina and/or silica aerosol volume fractions was studied. For application for solid rocket motor insulation, Reinforcement of EPDM with KP improves the performance of the material with respect to mechanical properties and thermal properties (thermal conductivity) while not improving well the performance with respect to ablation resistance. Using hybrid reinforcement content (KP + Al + Si) inside EPDM improves the performance of EPDM with respect to mechanical properties, thermal properties, ablation resistance and decomposition resistance. The best volume fraction which gives the best performance of the insulation material is 10 Phr KP + 5 Phr Al + 5 Phr Si. A new type of insulation material using the hybrid reinforcements was developed for the first time.