Aspen Times Weekly: Polartec ‘Delta’ Cooling Fabric |

Aspen Times Weekly: Polartec ‘Delta’ Cooling Fabric

by Stephen Regenold

A water-soaked cotton T-shirt has long served runners looking to cheat the heat. Moisture and moving air creates a cooling effect, with wet shirt fabric a stand-in for sweat on naked skin.

But clinging cotton is far from comfortable, and hot-weather exercisers more often default to polyester, nylon and synthetics touted to wick sweat as you bike or run.

As a new option this year, Polartec LLC launched a fabric called Delta. It’s advertised to “cool you down in the hottest conditions” via a tangle of fibers that hold water yet let the fabric breathe.

Polartec is known mostly for its fleece and cold-weather apparel. Delta is the company’s first warm-weather play.

I tested it for a month in heat up to 100 degrees. The material, which soon debuts in shirts from multiple brands, is knit with a raised texture designed to manage heat.

Unlike treated or chemical-based cooling shirts, which can feel cold to the touch, the Delta effect is more than skin deep. The company calls it “metabolic cooling” versus the “sensory cooling” offered by many brands using a treatment that feels cold when wet.

With Delta, no chemical treatments are used. Polartec instead knits together hydrophobic and hydrophilic fibers, the contrasting result dispersing moisture, increasing airflow and (unlike wet cotton) reducing friction against the skin when you move.

In my review, where I biked and ran in Delta shirts, sweat soaked into the fabric, allowing for noticeable cooling. It was especially prevalent on a bike, where stronger air movement perpetuates the effect.

While running, the technology was not as obvious. But the shirt remained comfortable even when soaked through with sweat, its raised texture never clinging.

I’ve long been a proponent of the “run wet” philosophy in summer. With Delta, Polartec gives an option for anyone in need of an edge in hot temps.

Look to brands including Outdoor Research, Westcomb, Kitsbow and Velocio to adopt Delta this year. The fabric is no panacea in the heat. But give the material a try this summer on the hottest days. You may never run “dry” again.

Stephen Regenold is founder and editor of

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