In our paper, Eq. 6(b) is applicable only at small strain, not the entire strain range covered in the study. In the more general case, the average deformation gradient is determined by the boundary displacement, but not the strain. It is also noted that there should be a factor of 1/2 in the definition of strain in Eq. 6(b). Finally, “strain” on the abscissa of Figs. 6, 7, 11, and 12 is the engineering strain (stretch ratio minus one). Readers may wish to convert to the “true strain” (ln(stretch)) or the Green strain (0.5×(stretch ratio squared minus one)) at larger strains. Although this correction has no qualitative effect on the paper's results, readers should be aware of the definition of strain if planning on using the results in a quantitative study.