By Leslie Tamura
Tuesday, August 10, 2010; HE03
Most of us are familiar with dry-wick athletic apparel. We see the advertisements claiming that this shirt has the textile technology to keep you dry, that those shorts can wick away your sweat, that this fabric will keep you feeling cool and comfortable during the most intense workouts.
But what's the science behind these promises? How do dry-wick textiles actually work?
It comes down to two principles: percolation and evaporation. "Moisture-management" fabrics absorb the sweat from your body, propelling it away from your skin, then spread it throughout the garment so it can easily vaporize into the environment.
But these products differ in how they use various fibers. A natural fiber may absorb more than a synthetic fiber, but a synthetic fiber may dry faster. Searching for the desired balance between wicking and drying, manufacturers mix different amounts of natural and synthetic fibers or transform an individual fiber's silhouette. The fiber recipe determines how the overall garment copes with sweat.
Natural fibers tend to love water. They pick it up whenever they can. Synthetic fibers, however, do their best to avoid or repel water.
Cotton is a natural fiber and a fantastic lover of water. When you sweat, cotton fibers will absorb the fluid, "wicking" the droplets away from your body. But because cotton fibers love liquid so much, they don't give it up very easily. The cotton fabric will hold onto the water, absorbing moisture into its fibers, resisting evaporation.
This is why it takes so long for your cotton T-shirts to dry.
"With natural fibers, you get what Mother Nature makes, and you have to live with it," said Becky Rose, an activewear research and development fellow for Invista, the manufacturer of Coolmax fabric. "Sometimes it's good, sometimes it's not so good."
Wearing a cotton shirt during a workout may feel cool because you're essentially wearing a shirt drenched in your bodily fluids, but as your core body temperature comes down, you may experience post-workout chills. Your cotton shirt does not want to dry, and you're left feeling cold and clammy.
"For athletic wear," said Yiqi Yang, a professor of textile chemistry at the University of Nebraska at Lincoln, "you want [the fabric] to wick water as good as cotton, but you don't want it soaked."
At the other end of the spectrum is polyester.
Polyester wants nothing to do with water. Its synthetic fibers are not tempted to absorb the beads of sweat pooling along your skin. When you do sweat, a 100-percent polyester shirt will simply trap the beads of sweat against your skin, often forcing the liquid to just trickle down your body. Polyester may just leave you feeling wet.
"Sweat is not just water on your skin," said Chris Moore, general manager of Optimer Brands, the manufacturer of DriRelease fabrics. "It is the transportation media of your body's excess heat."
If the polyester fibers don't remove the sweat, or heat, efficiently from your body, you may not cool as quickly as if you were wearing a cotton shirt.
Nylon is an in-between fabric, sharing properties with cotton and polyester. When nylon gets wet, it absorbs moisture, but it is also more apt to give up the moisture through evaporation. It takes less energy to release the water into the environment because the fibers don't really care if the water stays or goes.
But many athletic garments are made of 100-percent polyester fibers. How are they able to keep you feeling dry?
Some companies alter fibers' chemistry or apply a laminate to the outer surface of the fibers so they are more absorbent.
Other dry-wick garments are made of a blend of enough water-loving fibers to pull sweat from the body and enough water-hating fibers to throw water out onto the surface of the fabric for evaporation.
DriRelease, for example, uses a patented mix of 85-percent polyester and 15-percent cotton fibers in its fabrics. Its fibers can be found in such brands as Asics, Hanesbrands, Nautica and Nike.
Coolmax, the original moisture-management fabric developed by DuPont in 1986, features a unique 100-percent polyester fiber design.
Unlike other polyester fibers, which are typically tubular, Coolmax polyester fibers have either scalloped-oval or four-leaf-clover cross sections that create tiny tunnels for the sweat to slide through to the outside of the fabric.
"The smaller the diameter, or the finer the tubes," Yang said, "the more powerful the liquid transportation."
As more companies highlight their garments' absorbent capillaries, fiber blend and dry-wick, moisture-wick or quick-dry abilities, the athletic apparel market can get confusing.
"What's very important to communicate to consumers is to really look at the tag," Moore said.
If you want your garment to simply wick the sweat, 100-percent cotton would do well. If you want your garment to wick and dry, find a 100-percent polyester fabric with sufficient pores to allow for breathability. Or find a fabric with a blend of natural and synthetic fibers.
Because there are no industry-wide standards for rating moisture-management clothes, people have to make do with figuring out what they want from their workout attire and reading garment labels.
"You want a material that doesn't wet itself," Yang said, "but at the same time, it will transport water away from the body and not let the water in."