<p>The present manuscript explores the application of first-order similitude to structures subjected to impact loading. This method, introduced in a previous study, addresses the limitations of standard similarity principles when dealing with variables of the same dimension, enabling the use of different materials for the model (scaled structure) and the prototype (full-size structure). However, despite its advantages, this technique lacks a framework for evaluating material compatibility, which can affect the model accuracy. To address these limitations, this work integrates a material similarity approach with first-order similitude to assess the compatibility between the materials of the model and the prototype. The proposed methodology is evaluated through two case studies: An analytical model of a tube subjected to axial impact, and a numerical simulation involving two plates clamped together at top and bottom and struck by a rigid mass. The results reveal that using compatible materials can reduce the similarity distortion in first-order similitude, while the use of incompatible materials may lead to substantial inaccuracies of the model, with errors exceeding 35%. Additionally, the numerical simulations show that incorporating material similarity helps to resolve an incompatibility issue in the model, which was not identified in first-order similitude.</p>