We can’t all afford $750 solar-powered jackets to keep us toasty when the mercury takes a swan dive, but when the alternative is to bundle up with more layers than an onion-fanciers’ convention, Uniqlo’s supremely affordable, lightweight heat-generating innerwear for men and women appears nothing short of inspired. So does the HeatTech fabric that absorbs your body’s moisture and converts it to heat—at first blush, anyway.

Uniqlo Heattech, eco-fashion, green fashion, sustainable fashion, human-powered textiles, climate-controlled clothing, heat-generating clothing

Launched in 2006, HeatTech has since become a winter wardrobe staple in Japan; almost 20 million units were sold last year alone, according to Uniqlo. The fabric is woven from a specially designed hollow fiber thread that traps pockets of warm air, insulating your body in the same way a heavier wool would but without the bulk. Milk proteins, containing natural amino acids, are added to the fibers to create a soft, smooth hand.

Hollow fiber threads trap pockets of warm air, insulating your body like wool does.

More’s the pity then that the HeatTech fabric includes a mix of rayon, a man-made fiber created from cellulose that is eminently chemical-intensive and polluting, to turn your body’s perspiration into heat. (We’re not crazy about the antibacterial agent, a euphemism for “pesticide,” either.)

Although the downsides don’t detract from the promise of human-powered textiles, until the day comes when sustainable climate-controlled clothing becomes au courant, we’ll stick to the Jimmy Carter school of staying snug. Pass the parka?

+ HeatTech $10.50-$15.50

+ Uniqlo