## Materials and Methods
### Preparation of Functional Composite Yarns and Functional Elastic Knits  
In order to examine the influences of wrapping and twisting processes on the properties of the functional elastic knits, bamboo charcoal yarns and quick-dry yarns were twisted into twisted yarns using a rotor machine, while the other batch was wrapped into wrapped yarns using a hollow spindle spinning machine. During the process, the twist number was obtained based on the rotating speed difference between the winding and take-up processes. Tables 1-3 show the compositions, parameters, and specifications of wrapped/twisted functional composite yarns. Figure 1 shows the diagrams of a rotor spindle machine and twisted yarn. The bamboo charcoal yarn and the quick-dry yarn were intertwined evenly to form a spiral structure (Figure 1B) using a rotor spin device. Figure 2 shows the assembly of a hollow spindle machine and the structure of a wrapped yarn. A bamboo charcoal yarn and quick-dry yarn were wrapped in two manners, where the bamboo charcoal yarn was the core and the quick-dry yarn was the sheath, and otherwise. Figure 1: (**A**) The assembly of a rotor spindle machine and (**B**) the structure of a twisted yarns [26]. Figure 2: (**A**) assembly of hollow spindle machine and (**B**) diagram of a wrapped yarn [26]. The twist number is computed using the differences in the rotary speed of the package device and take-up roller. The equation is as follows. \[\text{Twist number}=\frac{\text{R}}{\text{T}\times\text{D}\times\pi} \tag{1}\]  
where R is the rotary speed of the rotor spin device or hollow spindle machine (r.p.m. ), T is the rotary speed of the take-up roller (r.p.m. ), and D is the diameter of the take-up roller (inch). Functional elastic knits are made with functional composite yarns using a crochet machine. The knits are composed of polyester filament as the warp yarns, rubber thread as the warp inlay yarn, and functional composite yarns as the wet inlay yarn (Figure 3). A total of six types of wrapped yarns and three types of twisted yarns, seen in Table 2. The pure bamboo charcoal yarns and quick-dry yarns serve as the control groups. The fabric specifications are shown in Table 4. \begin{table}
\begin{tabular}{c c} \hline
**Code** & **Compositions** \\ \hline Bamboo charcoal yarn & Combination of two 75D bamboo charcoal yarns without twisting or wrapping. \\ Quick-dry yarn & Combination of two 75D quick-dry yarns without twisting or wrapping. \\ Q-wrapped yarn & The wrapped yarns have one 75D bamboo charcoal yarn as the core and one 75D quick-dry yarn as the sheath. \\ B-wrapped yarn & The wrapped yarns have one 75D quick-dry yarn as the core and one 75D bamboo charcoal yarn as the sheath. \\ B/Q-twisted yarn & The twisted yarns are composed of 75D bamboo charcoal yarn and one 75D quick-dry yarn. \\ \hline \end{tabular}
\end{table} 
Table 1: Composition of functional composite yarns. Q: Quick-dry, B: Bamboo charcoal, and D: Denier. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample Code** & \multicolumn{2}{c}{**Twist Number (T.P.I.)**} \\ \hline Bamboo charcoal yarn & & N/A & \\ Quick-dry yarn & N/A & & \\ B-wrapped yarn & 20 & 25 & 30 \\ Q-wrapped yarn & 20 & 25 & 30 \\ B/Q twisted yarn & 5 & 10 & 15 \\ \hline \end{tabular} Note. For twisted yarns, a twist number that was above 15 T.P.I. (twists per inch) caused a high friction between the twisted yarns and the machine, leading to damage to the surface of the twisted yarns. Twist numbers of 20–30 T.P.I. were excluded from the production of twisted yarns. For wrapped yarns, a twist number was below 20 T.P.I., the hollow spindle spinning machine rendered a take-up extension beyond the tolerance of the wrapped yarns. Twist numbers of 5–15 T.P.I. were thus excluded from the production of wrapped yarns.  
\end{table} 
Table 2: Parameters of wrapped/twisted functional composite yarns. Q: Quick-dry, B: Bamboo charcoal, and D: Denier.