Abstract: A yarn is provided with a hollow fiber including a plurality of filaments and one or more longitudinal voids between the filaments; and a heat retention fiber being a fiber for emitting infrared light, the heat retention fiber including a plurality of filaments each being capable of retaining heat, the filaments having nanoscale powder capable of emitting near and far infrared light uniformly formed therein. The hollow fiber and the heat retention fiber are twisted together to form a yarn having heat retention capability.