"Heat-generating" fibers developed by Japanese textile manufacturers utilizing the water-absorbing, quick-drying functions of artificial fibers are warming up the underwear market.

Etsuyo Aoyagi, 34, a fashion-conscious woman who hails from ski country in Niigata Prefecture, said she was surprised at the warmth of the new underwear she purchased to fend off the cold.

"Unlike conventional bulky underwear, this is thick and good for layering," Aoyagi said.