In this work, the Finite Element Model Updating (FEMU) inverse analysis is used to identify heterogeneous material properties in nonlinear Kirchhoff-Love shells. The fundamental component of the proposed framework is the distinction between the discretization of the Finite Element (FE) forward problem and the unknown material fields [1]. To discretize the FE problem, the isogeometric (IGA) formulation described in [2] is used, while the material fields are approximated with low-order (constant or bilinear) Lagrange elements, referred to as the material mesh. The material mesh enables the capture of material fields with their discontinuities independently of the smooth IGA mesh and can reduce the number of unknowns for large FE models. In addition, a proper material mesh can prevent overfitting in the identification. The inverse problem is formulated as a least squares error objective function, which expresses the difference between FE displacements and experimental data. To minimize the objective, a local optimization with a trust-region method incorporating analytical sensitivities is used. The framework is validated through several numerical examples, in which high-resolution FE analyses with random noise are used as experimental-like data. The approach is tested for various forward problems, such as nonlinear statics with external loading, modal dynamics, and contact. The results indicate that given a sufficient amount of experimental data and appropriate FE and material mesh, the framework can efficiently reconstruct material fields with high precision, overcoming discontinuities and error sources such as noise or inaccurate input parameters. [1] Borzeszkowski B, Lubowiecka I, Sauer R A. Nonlinear material identification of heterogeneous isogeometric Kirchhoff–Love shells. Computer Methods in Applied Mechanics and Engineering. (2022) 390:114442. [2] Duong T X, Roohbakhshan F, Sauer R A. A new rotation-free isogeometric thin shell formulation and a corresponding continuity constraint for patch boundaries. Computer Methods in Applied Mechanics and Engineering. (2017) 316:43–83.