This article presents the authors’ comprehensive evaluation of the application of specific foam thermal insulation materials, namely expanded polystyrene (EPS) and extruded polystyrene (XPS), within railway substructures. The assessment extends to real-world conditions on the tracks of Slovak Railways (ŽSR), which share substantial similarities with other countries’ railway networks. The assessment of structural composition and material selection considers these technical aspects, while technological feasibility and the environmental implications associated with material production, delivery, and incorporation into railway construction do not. Additionally, the thermal insulation materials’ qualities are compared against conventional railway substructure materials. In these conventional setups, the thermal insulation layer often incorporates crushed aggregate of specified fractions and parameters in line with legislative standards. This article complements previous research conducted at the University of Žilina, focusing on the application of various thermal insulation materials within railway substructures. These materials were both experimentally tested (scale of 1:1) and numerically modelled, with results previously published by the authors. The published works detail the utilisation of diverse thermal insulation materials in railway substructures, primarily evaluating two crucial technical parameters: the protection of the subgrade surface against adverse effects of frost and, secondarily, their impact on the deformation resistance of the railway substructure.