Systematic review of thermal insulation materials and methods in high-speed rail systems

High-speed trains operate under significant thermal constraints that affect both energy consumption and passenger comfort. This systematic review examines the state of research on thermal insulation materials and approaches in high-speed rail systems. A systematic examination of existing studies is performed to delineate the primary families of insulation materials, their application domains, and assessment methodologies across four principal categories. Despite the diversity of topics addressed, the literature remains sparse, fragmented, and lacking in standardized methodologies. The results show increasing interest in new insulation options, particularly advanced materials such as phase change materials, aerogels, and multilayer designs, along with notable discrepancies between model predictions and real-world performance. Key trade-offs related to thermal performance, safety, durability, and operational constraints specific to HSR applications were discussed. Based on this synthesis, this review highlights both the potential of emerging insulation technologies and the urgent need for more comprehensive research, including experimental studies, real-scale validations, and harmonized assessment methods under realistic high-speed rail operating conditions.