Which Materials Absorb the Most Water?

A novel material called upsalite is the world’s most water-absorbent material. Made of nanostructured anhydrous magnesium carbonate, this material is capable of absorbing several hundred times its weight in water, even in low-humidity conditions. Other record-breaking water absorbent materials include sodium methacrylate, hygroscopic zeolites and poly(N-isopropylacrylamide)-coated cotton fabrics.

Polymeric superabsorbent materials are usually shaped as nets or meshes at the molecular level. These net-shaped structures are often elastic, enabling them to expand and absorb large quantities of liquid relative to their own masses. These materials are also hydrophilic, or water loving, enabling them to attract and retain water in these meshes. Polymeric superabsorbent materials are capable of absorbing hundreds of times their own weight in water, allowing them to become 99.9 percent liquid and still retain their form. Their absorbency depends on the salinity of the solution in which they are placed. The more saline contained in the solution, the lower the absorbency becomes. These materials are most commonly used in disposable personal hygiene products, such as adult protective underwear, sanitary napkins and baby diapers.

Superabsorbent materials that are not polymeric, such as cellulose-based fabrics, attract and retain water using a different mechanism. They are made up of hydrophilic fibers, but they do not store water in the actual fibers themselves. Instead, these fibers attract the water into the material, where it is stored in the empty pores between adjacent fibers.