This is a water-soluble adhesive which binds the fibres of the paper together and provides the stiffness. Damping the paper dissolves the sizing, separating the fibres and leaving the paper floppy and malleable. The reverse occurs as the paper dries out, setting the fibres in whatever position you require. In general, the thicker types of paper are best, such as artists' Ingres paper. As a technique however, wet-folding is still shunned by many folders because of the associated drawbacks.
Dampened paper is notoriously difficult to handle and easy to tear.
The loosened fibres will separate very easily, especially where several layers need to be folded simultaneously. The paper also expands unevenly in the direction of the fibres, so accurate folding is also a problem. In addition, due to the thickness of the paper, complex folds and large numbers of layers are impossible. Aside from the ability to mould the paper into a more lifelike shape, wet-folding provides two other main advantages. Assuming that the sizing and colouring within the paper is chemically neutral, the fold will also last for years, as with many other true works of art.