Absorbent fabrics are hydrophilic, meaning they attract water. Water attraction is called hygroscopy. Natural fibers like cotton, hemp and bamboo are made of cellulose, whose sugar molecules can break water's surface tension so that it moves into the spaces between fibers, and into the fibers themselves. In contrast, synthetic fibers like polyester don't break the surface tension, so they don't absorb water the same way. New man-made fabrics combine materials to create much more absorbent fabrics.

The Most Absorbent Fabric Is a Combination of Materials

A composite fabric marketed under the brand name Zorb combines several materials including tangled cellulose fibers and poly microfibers, though the exact combination is a trade secret. According to the Cloth Diaper Testing site, the material performed best in tests of absorbency and ability to prevent leaks when compressed. The proprietary manufacturing process makes it more absorbent than any one of its constituent components alone, but because it isn't woven it must be sandwiched between layers of some woven fabric.

Cotton Is the Best-Known

Cotton is plant fiber which, after processing, is 99 percent cellulose. As Cotton Incorporated describes it, the structure of the cellulose forms microscopic chains. Water is absorbed into the cellulose through capillary action, which is the absorption and movement of moisture between and among fibers. By "wicking" through capillary action, each fiber acts like a sponge to hold water. Individual fibers are spun together into threads. When the threads are woven into loops, as in a terrycloth towel, there is more thread length per square inch than in a plain cotton sheet, so terrycloth absorbs more moisture.

Bamboo and Hemp May Surprise You

Bamboo and hemp are also cellulose fibers, so they can absorb water in a manner similar to cotton. Tests published in the Indian Journal of Fibre and Textile Research show that bamboo is able to retain almost twice as much moisture as organic cotton alone, although it wicks more slowly. A bamboo/cotton blend combines the advantages of both. The Natural Baby Co. describes hemp as more hygroscopic than cotton, though because it wicks more slowly, hemp too performs best when blended with cotton.

Microfibers Offer Another Approach

While synthetic fibers by themselves can't absorb water the way natural cellulose fibers do, splitting them into microfibers creates pores and much more surface area between fibers. They absorb water through capillary action among fine parallel fibers in the fabric, as described in the Textile Research Journal. The absorbent characteristics vary with the splitting method used. These fabrics are also suited to absorbing dirt and grime along with moisture.