## 3 Results and Discussion
### Effects of Twist Number on the Air Permeability of Functional Elastic Knits  
Doing exercise accelerates metabolism and demands 20% of the total energy consumed by metabolism. At the same time, the rest 80% is dissipated via the form of heat. If the human body fails to dissipate heat in a short time, the core temperature of the body then increases by 5 \({}^{\circ}\)C every ten minutes. When the core temperature reaches to a certain point, the human body perspires in order to attain a thermal balance [11]. This phenomenon leads to dehydration, and the air permeability of the elastic knits is thus a crucial factor in terms of the comfort on the skin [27; 28].  
Figure 8: Bursting stress of elastic knits as related to parameters of different functional yarns. The error bar indicates the SD.  
Figure 9: Images of the fractured elastic knits after the bursting strength test. As all samples exhibit similar failure over the surface, B/Q-twisted yarns made of 20 T.P.I. is used in this diagram.  
In comparison to the control groups (i.e., functional elastic knits that were composed of non-processed bamboo charcoal yarns or non-processed quick-dry yarns, the elastic knits that were composed of twisted yarns or wrapped yarns had a considerably higher air permeability. In addition, the analysis software of an optical microscope showed that the control groups had an average pore size of 0.03-0.04 mm\({}^{2}\), while the experimental groups (i.e., functional elastic knits) had an average pore size 0.08-0.1 mm\({}^{2}\). There were no distinctive variations in the thickness and weight of the knits when the diameter of the yarns decreases. The results were ascribed to the fact that the thickness and weight of the elastic knits were primarily based on the amount of rubber threads. Therefore, using different wrapped yarns or twisted yarns did not noticeably change the weight and thickness of the elastic knits.  
Regardless of whether it was bamboo charcoal yarns or quick-dry yarns, they had a fluffy structure. When they were used to produce elastic knits using a crochet machine, the knits demonstrated a shrinkage when they were off the pre-tension force exerted by the machine. Therefore, the pores of the elastic knits were compressed as seen in Figure 10A,B. The wrapping or twisting process made the structure of yarns compact, resulting in a smaller diameter. Therefore, the resulting elastic knits had a larger pore size as seen in Figure 10C-K. Previous studies indicated that the variations in the diameter of yarn as well as variations in the thickness and weight of the knits affected the air permeability of the knits. In comparison of Table 2 and Figure 11, the air permeability of the elastic knits was inversely proportional to the diameter of yarns. This result was in conformity with that of previous studies [12; 29].  
Figure 11: Air permeability of functional elastic knits in relation to the administration of a wrapping/twisting process as well as the twist number of the yarns. The error bar indicates the SD.  
Figure 10: Surficial observation of the functional elastic knits that are made of **(A)** quick-dry yarn; **(B)** bamboo charcoal yarn; **(C)** 20 T.P.I. B-wrapped yarn; **(D)** 25 T.P.I. B-wrapped yarn; **(E)** 30 T.P.I. B-wrapped yarn; **(F)** 20 T.P.I. Q-wrapped yarn; **(G)** 25 T.P.I. Q-wrapped yarn; **(H)** 30 T.P.I. Q-wrapped yarn; **(I)** 5 T.P.I. B/Q-twisted yarn; **(J)** 10 T.P.I. B/Q-twisted yarn; and **(K)** 15 T.P.I. B/Q-twisted yarn. The small pore size is indicated in red drop-like triangles and the large pore size is indicated yellow drop-like triangles.