Thin sheets, from graphene to biological membranes, exhibit wrinkling, folding, and thermal deformations driven by geometric nonlinearities. They are treated using weakly nonlinear theories such as the Föppl–von Kármán equations, whose reliance on small slopes and a single-valued height field excludes large-slope and nongraph configurations even at small strain. We introduce a geometric reformulation in terms of scalar stress and curvature potentials that preserves the FvK structure while removing the graph restriction. We show that intrinsic symmetries of these potentials, as opposed to symmetries of the configuration, can persist when none is apparent in the embedding, enabling analytical solutions of boundary-value problems inaccessible to the conventional height-based formulation. Finite-element comparisons validate the predictions under strong confinement. Together, the extended validity and tractability open analytical routes to fluctuating membranes, ribbons, and architected sheets.

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• Elastic deformation
• Elasticity
• Mathematical physics
• Mechanical properties of membranes
• Surfaces
• Mathematical physics methods