2.3.1. FIR-Emitting-Pajamas Group
Subjects in this group were provided with two sets of FIR-emitting pajamas. The FIR pajamas were fabricated using two textile materials: pure cotton fibers and the proposed handmade FIR fibers with the FIR-emitting function. The proposed FIR function was provided via the physical modification of the fibers during the spinning process without having to add any chemicals. In addition, based on the theoretical knowledge and simulations, it was believed that better performances in far-infrared radiation absorptivity and emissivity would be induced due to the increased total internal reflection, as well as the transmission of fewer infrared waves within the cross-sections. To ensure the quality of the proposed pajamas with FIR features, their performance in terms of FIR emissivity and temperature differences was evaluated and ensured in a certified testing lab based on the national standard method (GB/T 30127–2013) and requirements (the temperature difference had to not be less than 1.4 °C and the emissivity had to not be less than 0.88).