Why do wet-folded origami models become durable after they dry?

Wet-folding is a technique in origami that allows folders to create soft, organic curves and highly realistic forms. The durability of these models after they dry is due to the presence of sizing—a water-soluble glue or binding agent—within the paper fibers.12

When the paper is dampened, the moisture softens the fibers and temporarily weakens the natural interfibre bonds, which are typically maintained by hydrogen bonding or van der Waals forces. This flexibility allows the folder to shape the paper into complex, curved structures that would be difficult to achieve with dry paper. As the water evaporates, the sizing agent hardens and the fibers re-bond, locking the paper into its new, rigid shape and providing the model with its final durability.21