The results of this article are accepted as a provisional patent by a unisearch limited of the University of New South Wales in Australia in 1994. The low-impact behavior of polyamide 11 when modified by a butadiene-acrylonitrile copolymer ("nitrile rubber") was studied. The effect of the level of rubber addition and the acrylonitrile content is described. The rubber particle size and particle-size distribution were found to be important factors in controlling blend properties, including impact strength. SEM studies showed that toughness can be predicted by morphology. The mechanism of energy dissipation at low concentrations of rubber (greater than or equal to 20%) is crazing, plastic deformation, voiding, and matrix shear yielding. On the basis of these studies, it can be concluded that toughening of polyamide 11 is possible with nitrile rubber and that these blends are industrially compatible.