Natural sodium bentonite has high expansibility (its particles can expand to 10–30 times their original volume upon water absorption). When the bentonite waterproof blanket comes into contact with water, the sodium bentonite absorbs water and expands. Under compressive forces (from the substrate, temporary protective layers, backfill soil, and internal tensile fibers), its molecules interlock and internal voids shrink, forming a dense gel-like structure. This prevents water molecules from passing through, achieving waterproofing with a permeability coefficient of 5×10−11 m/s5×10 −11 m/s. The greater the compressive force, the higher the density and the more effective the waterproofing.