Fire-sealing gap filler is an eco-friendly single-component fire-sealing material that quickly and effectively seals hard-to-reach gaps. It is suitable for joint seals between curtain walls and floor edges, as well as gaps with high elongation. It boasts good air and water tightness, excellent elasticity, and does not crack upon use. When heated during a fire, it expands rapidly, sealing the gaps left by the combustion of combustible materials within the fire. This prevents the spread of flames and smoke through the curtain wall, minimizing the extent of fire damage.