Reactive polyurethane hot melt adhesive (PUR) is solid at room temperature and is heated into a molten state before dispensing. It is a one-component, solvent-free structural hot melt adhesive that achieves high initial bonding strength through physical solidification. Subsequently, it reacts with moisture in the environment (from the substrate or air), initiating a chemical crosslinking process that cures into an elastomer. After curing, it provides stronger bonding strength along with excellent moisture resistance, heat resistance, and chemical resistance.