An object is to provide a fiber that absorbs heat with good efficiency, has excellent transparency and heat-retaining properties, and does not compromise the design characteristics of a textile product, and to provide a textile product in which the fiber is used. Hexaboride nanoparticles, a dispersion medium, and a dispersion agent for dispersing the nanoparticles are mixed together. The mixture is dispersed and dried to obtain a dispersion powder. The resulting dispersion powder is added to thermoplastic resin pellets, uniformly mixed, and thereafter melted and kneaded to obtain a master batch containing a heat-absorbing component. The master batch containing a heat-absorbing component is mixed with a similarly prepared master batch to which inorganic nanoparticles has not been added, and the mixture is melted, spun, and drawn to manufacture a multifilament yarn. The multifilament yarn is cut to fabricate staples, and the staples are used to manufacture a spun yarn having heat-absorbing effects. The spun yarn is used to obtain a knitted product having heat-retaining properties.