AbstractStress softening (Mullins effect) occurs in rubber vulcanizates during the first and subsequent deformations. This paper shows the similarity of the degree of stress softening in both unfilled and carbon black‐filled vulcanizates of natural rubber when stressed almost to break. This confirms the earlier investigations which were confined to moderate stresses. A simple interpretation of the tensile stress–strain results for filled rubber is that the strain in the rubber is increased by the presence of the filler, so that the ratio of the average strain in the rubber to the measured overall strain is given by a strain amplification factor. The usefulness of this concept is confirmed by showing the similarity of the stress‐softened curves after normalizing the strains, provided the vulcanizates of both gum and filled vulcanizates were subjected to the same initial s
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