The Stirling engine is mainly composed by five compartments: two working spaces and three heat exchangers (heater, cooler, and regenerator). The regenerator (porous medium) characteristics, especially material and porosity, are determinant for the whole engine performance. In order to choose the adequate regenerator, numerical and experimental methods can be adopted. Numerical models, i.e., isothermal, adiabatic, and quasi steady, are applied to determine the engine performances considering the regenerator parameters. The most powerful numerical tool is the computational fluid dynamics (CFD) simulation, which allows a detailed examination of flow behavior through the porous media. The one-variate experimental method is generally considered to test regenerator operation in the Stirling engine but the figure of merit (FOM) formulation and the experimental design methodology are more precise and faster to compare several regenerators performances.