Firestop gap sealant is an environmentally friendly one-component firestop material that can quickly and effectively seal hard-to-reach gaps. It is suitable for joint sealing between curtain walls and floor edges, as well as for gaps with high elongation. It boasts excellent airtightness, watertightness, and elasticity, preventing cracking upon use. In the event of a fire, it expands when heated, quickly and effectively sealing the gaps left by the combustion of flammable materials. It prevents the spread of fire and smoke through the curtain wall, reducing the extent of fire damage.