The driving forces behind a superabsorbent polymer's water absorbency are osmotic pressure and hydrogen bonding. The difference in the sodium ion concentration between the inside of the polymer and the solution in which it is immersed causes the water to flow in rapidly, trying to balance the number of ions inside and outside the polymer. Also, the polymer chains are lined with carboxyl groups (-COOH) with about 50 to 70% of these in the sodium salt form. In contact with water, the carboxyl groups dissociate into negatively charged carboxylate ions (-COO-). These form hydrogen bonds with water molecules.





In addition, these carboxylate sites repel each other, which widens the polymer network, thus allowing more water to be absorbed. However, the crosslinked polymer molecules can only stretch so far. Therefore, the amount of water absorbed is in part determined by the balance between widening of the polymer network as hydrogen bonds form and "elastic pressure" of the crosslinked molecules.

The electrolyte concentration in the water being absorbed greatly affects the amount of fluid that can be absorbed by the polymer. The ions of the electrolyte act as "contaminator" ions and become positioned along the polymer chain at the carboxylate sites. The electrolyte ions partially neutralize these sites and limit the potential sites for hydrogen bond formation between the polymer and water molecules. In addition, there will be less repulsion between the crosslinked chains of the polymer, thus enabling less water to be absorbed. Also, the presence of these ions decreases the unbalance which "drives" osmotic pressure.

A typical superabsorbent polymer may absorb about 400 times its own mass of distilled water while absorbing almost 300 times its mass of tap water. The same polymer may absorb only 30 to 40 times its mass of 1% sodium chloride solution.