This chapter proposes a novel model for the gas humidification process in a fuel-cell assembly as a benchmark for estimation and control-oriented tasks. The text delves into the benchmark’s origins, its importance, and the challenges it poses to control engineers. The problem description offers a detailed overview of the assembly designed to provide gases to a fuel-cell with controlled humidity and temperature. The deduced mathematical model is described, emphasizing the use of a Phenomenological Based Semi-physical Modeling (PBSM) approach, which is an intuitive and simple method for deducing models. Key assumptions and simplifications are outlined for clarity. The chapter also details the experimental setup and the performance metrics used for evaluating control systems, providing a comprehensive view of the benchmark’s design and associated limitations. The access to the benchmark’s resources is easy through a web repository, containing both MATLAB® and Python scripts to solve the whole model. Potential users are guided on how to access and run the benchmark. Future research directions and existing approaches to solving this problem are discussed, identifying gaps in the current state of the art. Finally, the references cited in the chapter are listed to enrich the reader’s understanding.