Reinforced nitrile-butadiene rubber by aramid fibers and polyacrylonitrile fibers was investigated as flexible ablative materials. Erosion resistance of the ablative materials reinforced by both fibers was greatly improved. Comparing to the physical reinforcement, confinement effect of fibers plays a more important role for the improved erosion resistance of the ablative materials. Four different layers, including virgin material, pyrolysis layer, loose carbon layer and dense carbon layer were formed inside the ablative materials during the pyrolysis process, and aligned gas channels were observed in the two carbon layers. The aligned gas channels were formed through the aid of fibers, and they facilitated the release of high pressure inside the composites as well as helped strengthen the pyrolysis gas flow discharged out of the ablative materials, which greatly contributed to the improved erosion resistance of the composite. [ABSTRACT FROM AUTHOR]