Theoretical, numerical, and experimental results from a unidirectional strain–limiting structure. a) Bilinear stress–strain curves of 1 μm-thick PI film on 1 mm-thick Silbione substrate subjected to various prestrains. b) The transition strain versus the prestrain for the PI film on several substrates with thickness ratio H/h = 1000. c) The tangent modulus normalized by the substrate modulus, Ētangent/Ēs, versus the normalized film modulus Ēf/Ēs for several thickness ratios H/h. d) The critical film length that separates local wrinkling from global buckling. e,f) Numerical results and optical images (scale bar, 1 mm) of the morphology and out-of-plane displacement for a 1 μm-thick PI film on a 1 mm-thick Silbione substrate subjected to 15.1% prestrain.