This blog post explores how functional fibers like Coolmax rapidly wick away sweat and maintain body temperature through their fiber structure and scientific principles.
Intense exercise leading to heavy sweating can soak clothing, reducing its functionality. The damp feeling may cause discomfort, and the weight of sweat can hinder an athlete’s performance. This not only lowers exercise efficiency but can also affect long-term body temperature regulation. The more sweat produced, the faster heat is drawn from the skin’s surface, potentially causing the body to cool too quickly. This problem becomes particularly severe in cold environments. Without appropriate clothing in such conditions, the body’s energy expenditure increases, and fatigue during exercise can intensify.
Furthermore, on cold, windy days, sweat cooling down can steal heat from the body, potentially causing hypothermia in extreme cases. Wearing soaked clothing in the wind can result in up to 240 times more heat loss than wearing dry clothing. To address these issues, athletic wear must not only adapt to temperature but also help regulate body temperature by rapidly evaporating moisture. Consequently, the need for functional materials that effectively absorb moisture and quickly disperse it outward has emerged, and several have been developed. A prime example is ‘Coolmax’ developed by DuPont.
Coolmax is made from polyester-based materials that do not readily absorb moisture. Natural fibers like cotton, which possess many specific chemical structures that readily bond with water molecules, absorb moisture well but dry poorly when wet. In contrast, polyester fibers have almost none of these specific chemical structures, making them unable to easily bond with water molecules. Consequently, they absorb little moisture and remain dry. But if polyester fibers don’t absorb moisture well, how can they effectively wick it away? How does Coolmax fiber, made from polyester, manage to quickly transport sweat from the skin to the outside?
The secret lies in the cross-section of the extruded yarn. Chemical fibers like polyester are formed when molten liquid raw material passes through tiny holes, cools, solidifies, and takes the shape of a yarn. The initial yarn formed here is called the ‘filament,’ and the small hole it emerges from is called the ‘spinneret.’ The cross-sectional shape of the filament is determined by the shape of the spinneret. Coolmax yarn, formed by extruding through a cross-shaped spinneret, has a cross-section matching the spinneret’s shape, resulting in grooves running in all directions along the yarn’s sides. Fabrics woven from this yarn develop microscopic pores, increasing the surface area exposed to air compared to fabrics woven from yarn with a standard circular cross-section. Moisture contacting the fiber then escapes outward through these minute holes via capillary action.
Capillary action is the phenomenon where the surface of a liquid rises up a narrow, long tube when inserted into it. Examples include water absorption by plant roots or sponges, and alcohol rising up the wick of an alcohol lamp. In the case of Coolmax fibers, due to the adhesive force between the walls of the microscopic pores and water molecules, once the edge of the moisture begins to climb the wall, the cohesive force between water molecules causes the entire water surface to attempt to rise to the height of the edge water molecules. Through the continuous interaction of these two forces, all sweat accumulated on the skin can escape to the outside of the fiber and evaporate.
Coolmax fiber has an inherently low moisture retention rate, allowing it to evaporate moisture much faster than cotton fiber. Even when thoroughly soaked, the garment can be worn immediately after a quick wring and shake. This characteristic is highly practical for those engaged in frequent outdoor activities. Coolmax fibers are particularly useful not only for athletes but also for those who enjoy hiking and camping, as they maintain warmth in extreme environments while facilitating efficient sweat wicking. Furthermore, due to its synthetic fiber nature, Coolmax fiber offers excellent resistance to pests and outstanding antibacterial properties, making it easy to care for. It is widely used in t-shirts and various sportswear, and its ability to be freely blended with cotton yarn expands its applications to underwear and socks.
The physical properties of a fiber are not determined solely by its chemical composition but are also significantly influenced by the cross-sectional shape and thickness of the yarn, as well as the weaving method. Previously, clothing material development focused solely on microscopic, one-dimensional chemical structures. Recently, however, there has been an active movement to discover new functional fibers by appropriately modifying and combining the remaining fiber elements. Given this trend, it is no exaggeration to predict that creative materials like Coolmax fiber will continue to emerge.
Ultimately, functional fibers are evolving to meet the needs of modern people seeking comfort in their daily lives. Consequently, their potential applications extend beyond everyday wear and sportswear to various industries. At this juncture, where advanced material technology is bringing significant changes to all aspects of our lives, functional fibers will continue to develop and play a crucial role in enhancing the quality of human life.
