Owing to its technological relevance and widespread occurrence in biological systems, wrinkling in bilayers has been the subject of extensive study over the past decades (see [1], among many others). Such systems typically consist of a thin film perfectly bonded to a much thicker substrate, which is often idealized as isotropic. Consequently, the influence of substrate anisotropy - particularly under moderate to large strains - remains largely unexplored. In [3], we extend the small-strain framework of [2] by considering a fiber-reinforced substrate, where fibers are embedded in a hyperelastic isotropic matrix, and arbitrary elastic mismatch between the matrix and the film is allowed. Beyond the mismatch itself, the onset of wrinkling is shown to be strongly influenced by the fiber orientation, distribution, and the coupling between fiber stiffness and concentration. The film is modeled as an extensible elastic thin plate exhibiting bending stiffness and perfectly adhering to a hyperelastic, fiber-reinforced half-space. For the wrinkling onset, we derive novel scaling laws for the critical strain and wrinkling wavenumber. These scalings are valid across regimes in which the instability is governed either by the film (primal regime) or by the substrate (dual regime). That is, the analysis captures scenarios involving highly compliant substrates as well as cases where the film is only marginally stiffer—or even softer—than the substrate. The resulting framework strikingly moves away from the classical asymptotics established in [1, 2] for wrinkling occuring at small strains. A key finding is the emergence of an effective isotropization of the bilayer beyond a critical reinforcement threshold, which delineates the transition between the primal and dual regimes. REFERENCES [1] Cao, Y., Hutchinson, J. W., ”Wrinkling Phenomena in Neo-Hookean Film/Substrate Bilayers”, Journal of Applied Mechanics, 79, 031019 (2012). [2] Mirandola, A., Cutolo, A., Carotenuto, A. R., Nguyen, N., Pocivavsek, L., Fraldi, M. and Deseri, L.,”Toward New Scaling Laws for Wrinkling in Biologically Relevant Fiber-Reinforced Bilayers”, Journal of Applied Physics, 134, 154702 (2023) [3] Mirandola, A., Cutolo, A., Carotenuto, A.R., Palumbo, S., Fraldi, M. and Deseri, L., ”Unveiling scaling laws for wrinkling in fiber-reinforced bilayers at any elastic mismatch”, submitted