The building and construction industry heavily relies on the use of concrete and cementitious composites due to their exceptional attributes, including strength and durability. However, the extensive use of these materials has led to significant environmental challenges, including resource depletion, carbon emissions, and waste accumulation. In response to these challenges, recent advancements in fibre cementitious composites have shown promise in mitigating these detrimental effects. The integration of waste materials to supplement manufactured fibres represents a promising development in reinforced concrete composite materials. Waste materials like textiles and cardboard are emerging as potential fibre supplements in cementitious composites. While these materials have primarily been investigated for their mechanical characteristics, understanding their thermal properties when applied in construction materials is equally crucial. Incorporating fibres within composite designs often requires matrix modification to reduce degradation and enhance fibre longevity. This study aims to investigate the thermo-phase change properties of both textile and cardboard fibres within varied concrete matrices. Additive materials offer a range of advantages and challenges when used in composite materials, with additional complexities arising when incorporating fibre materials. Understanding the thermal reactivity of these materials is crucial for optimizing their application in construction. This study demonstrates the potential of waste fibres used with gypsum, metakaolin, and silica fume as matrix modifiers in concrete. This research provides valuable insights for future studies to explore specific material combinations and investigate complex fire testing methods, ultimately contributing to the development of sustainable construction materials.