The increasing housing shortage in Portugal, alongside the industrialisation of the construction sector, has driven growing interest in modular construction. This innovative method offers faster building times, cost efficiency, and reduced waste. However, despite its advantages, aspects such as the thermal performance of modular systems have often been overlooked in previous studies. This highlights the need for a deeper understanding of how modular construction materials can be optimised to address these challenges. This research focuses on the hygrothermal behaviour of various concrete compositions through the investigation of their performance under different environmental conditions, with an emphasis on relative humidity and thermal conductivity. Experimental tests were conducted to provide critical insights into how different concrete compositions react to temperature and moisture fluctuations. The results revealed that lower water content in concrete leads to a decrease in thermal conductivity. The results of this research can help optimize the design of prefabricated concrete panels to enhance thermal efficiency and hygrothermal performance. This would ensure more stable and comfortable indoor environments while minimizing energy consumption in modular buildings. By aligning material performance with sustainability goals, the research aims to support the broader objective of creating environmentally responsible, energy-efficient housing solutions. Ultimately, this work seeks to advance the understanding of concrete's hygrothermal behaviour, contributing to the development of sustainable practices and ensuring modular construction achieves a balance between performance, occupant comfort, and environmental sustainability.