What to wear to stay cool in the heat

AP:

When temperatures soar, dressing for the heat may seem simple. Choose something light, loose and breathable. But textile researchers say staying cool involves more than fabric. Weight, construction, fit and even colour can affect how well clothing helps the body manage heat, while the best choice also depends on your activity level and how much you sweat. As extreme heat becomes a growing public health concern, scientists are studying clothing designed to help people stay cooler. But what you wear is only one part of how the body responds to heat.

Clothing should allow the body’s natural response to heat to work, said George Havenith, emeritus professor of environmental physiology and ergonomics at Loughborough University.

“It’s a really powerful mechanism from humans that we can defend our body temperature with,” Havenith said. “The most important thing in the selection of clothing would be to make sure you do not hamper sweat evaporation.”

LOOK FOR LIGHTWEIGHT CLOTHING

In hot weather, choose lightweight clothing that allows air to pass through the fabric, helping sweat evaporate and keeping the body cooler. Researchers call this property air permeability. The fibre is only part of the equation. How the fabric is woven or knitted also affects how easily air can pass through it.

“For greatest airflow, open weave and loose knit structures are best, free of any water – or soil-repellent finishes. Cellulosic fibres, like cotton and flax (linen), tend to be more breathable and comfortable,” said Meredith McQuerry, a professor at Florida State University who studies clothing development and performance.

Linen can be a good option, but “linen” on the label doesn’t tell the whole story. She said shoppers shouldn’t rely on fibre content alone. A more open-weave structure will generally be more breathable, regardless of the garment’s fibre.

Wicking works differently. These fabrics move sweat away from the skin and spread it over a larger surface area, helping it evaporate faster. Engineered synthetic fibres are commonly used in sportswear, Havenith said.

But wicking does not necessarily mean cooling. Moving sweat away from the skin can make clothing feel drier, while evaporation farther from the skin may provide less direct cooling.

Fit matters too. Havenith recommends clothing with enough room for ventilation, particularly in hot outdoor conditions. But McQuerry noted that the best fit depends on the activity. Someone exercising outdoors may prefer a snug synthetic tank top, while someone sitting on a porch or doing light yard work may be more comfortable in a looser cotton T-shirt.

“In casual settings, wearers may prefer a looser fit that allows for more airflow while standing or sitting. If performing physical activity, a tighter fit may be preferred to enable quicker sweat evaporation,” said McQuerry.

COTTON OR POLYESTER

Choosing between cotton and polyester comes down to how much you expect to sweat and what you’ll be doing. Cotton absorbs sweat but can become heavy when saturated, while engineered polyester moves moisture across the fabric and dries faster, making it common in athletic wear.

During exercise, polyester can continue evaporating sweat, while cotton works well only until it becomes saturated, said Po-Chun Hsu, an assistant professor at the University of Chicago who studies materials and sustainability.

“Imagine you are wearing a wet T-shirt. Of course you get this evaporation going on, but then you also block the breathability, and you won’t feel very comfortable when it’s completely wet,” he said.

Polyester is widely used because it is inexpensive, durable and versatile, but not all performs the same way. Jonathan Chen, a professor at the University of Texas at Austin who studies textiles and apparel, suggests looking for lightweight polyester garments designed for breathability. A porous athletic shirt can behave very differently from a dense garment, even if both labels say 100 per cent polyester.

People spending extended time outdoors in direct sunlight should prioritise covering skin to protect against UV exposure and sunburn, Havenith said.

Loose, ventilated clothing can provide coverage while allowing airflow, such as a lightweight long-sleeved shirt.

Colour matters, too. White, light-coloured and highly reflective fabrics can reduce heat gain by reflecting sunlight rather than absorbing it, Hsu said.

Researchers have made significant progress in managing sweat and moisture, Hsu said, while developing clothing that reflects more sunlight remains an emerging area.

Consumers should also look beyond the word “cooling” on clothing labels. Some cooling fabrics are designed to create an initial cold sensation against the skin, Hsu said, but that effect can fade as the material warms.

“If it doesn’t really, let’s say, increase the evaporation of the surface area or reflect the sunlight or enhance the breathability, then it’s quite unlikely that it will have any continuous cooling effect,” Hsu said.

Some cooling approaches go beyond fabric. Fan-equipped clothing, increasingly used by outdoor and factory workers in Japan, circulates air beneath the garment to help sweat evaporate.

The clothing can improve comfort and lower skin temperature, Havenith said, but does little to lower core body temperature. Battery weight can also be a drawback, though that could change as battery technology improves.

For shoppers, the researchers’ advice comes back to looking beyond a single word on the label. Consider whether a garment is lightweight, how easily air moves through it, how it handles moisture, how it fits, whether you will be in direct sun and what kind of activity you will be doing.

There may not be one perfect fabric for extreme temperatures, but there are ways to choose clothing that works with the body’s cooling system rather than against it.

lifestyle@gleanerjm.com