Why does cotton absorb more water than nylon?

The difference lies in the simple yet fascinating molecular makeup of cotton, nylon, and water. Water's basic structure, with one oxygen atom bonded to two hydrogen atoms, reacts differently when interacting with the complex molecules that make up cotton and nylon.

Water’s sticky nature comes from its molecular arrangement. The oxygen atom has a slight negative charge, while the hydrogen atoms carry a slight positive charge. This dipole effect makes water molecules behave like magnets, sticking together and creating a slight elasticity at the surface of water droplets. It also means that water molecules will readily bond with other molecules that have an opposite charge.

Both cotton and nylon consist of large polymer molecules, which are essentially long chains of atoms arranged in repeating patterns. These polymers are densely packed with atoms, offering numerous sites where water molecules, with their sticky properties, can easily bond.

Cotton is composed of pure cellulose, a naturally occurring polymer. Cellulose is a carbohydrate, and its molecular structure consists of long chains of glucose (sugar) molecules. If you examine the structure of cellulose, you will notice the OH groups on the outer edges. These negatively charged groups attract water molecules, making both cellulose and cotton highly absorbent. Cotton can soak up about 25 times its own weight in water. Chemists refer to cotton as hydrophilic, meaning it attracts water molecules.

Nylon is a man-made material, meaning chemists design the polymer molecules that form nylon. A long chain of over 100 repeating units of carbon, oxygen, hydrogen, and nitrogen atoms makes up the nylon molecule. The strength of the long nylon chain made it an excellent replacement for silk, which had a similar texture and feel.

The nylon molecule also contains many sites where it can bond with water molecules, but it has fewer such sites compared to cotton. While nylon does absorb water, it’s much less efficient than cotton, absorbing only about 10 percent of its weight in water.

There are a few additional factors that help cotton towels and nylon jackets perform as intended. Terrycloth, the fabric used in towels, is covered in numerous loops, providing more surface area for cotton and water to interact. Textile manufacturers also treat nylon with resins and other water-repellent chemicals, causing water droplets to roll off rather than being absorbed.

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