# Breathable Materials for Triboelectric Effect-Based Wearable Electronics
## 4 Discussion  
The breathable materials summarized in this review comprise three types, namely fiber, textile, and nanofiber membrane-based wearables. Table 1 presents an overview comparison of the three types of materials. For breathability, fiber and textile-based devices have superiority over nanofiber membrane-based electronics. In contrast to textile and nanofiber membrane, the fabrication process of the fiber-based device is much more complex, as every single fiber is made up of an electrode and friction layer. For electronic devices that have higher requirements with sensitivity, the nanofiber membrane cannot be replaced by fiber or textile-based devices, which benefit from its nanostructure on its surface. Moreover, a nanofiber membrane is soft, lightweight, small, shape-adaptive, and easy to integrate. Therefore, for practical application, sensitivity, breathability, processability, and cost should all be taken into consideration when designing and fabricating wearable electronics.  
To sum up, Figure 9 depicts the summary of the breathable materials used to fabricate comfortable wearable electronics by replacing traditional airtight materials. To meet the requirements of comfort and skin friendliness, the components of clothes such as fibers and textiles were selected to fabricate wearable electronics, which are also low-cost and easy to integrate with clothes. Wearable electronics fabricated with nanofiber membranes are preferred due to relatively good air-permissibility and micro-nano structure, which guarantees both skin friendliness and sensitivity of the device. Single conductive fibers, metal mesh, conductive textiles, and networks made up of conductive nanomaterial  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Breathability** & **Processability** & **Materials Cost** & **Sensitivity** \\ \hline Fiber-based & & & & \\ Textile-based & & & & \\ Nanofiber & & & & \\ membrane-based & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of the breathable materials.  
Figure 8: Nanofiber membrane-based stretchable wearable sensor. (**a**) Schematic illustration of the structure of the stretchable wearable device (SWD). (**b**) The tensile property of the TPU NM collected on different substrates. (**c**) Manufacture process of the SWD. Figure adapted from ref. [57].  
are the commonly used air-permissive electrodes. Elasticity is another critical factor that influences the comfort of the devices, being is shape-adaptive and thus offering a better attachment to skin.  
The breathable materials and fabrication methods reviewed in this paper can be expanded to all wearable devices, which provide valuable references for the design and fabrication of skin-friendly devices. However, effects are still needed to realize superior air-permissibility, higher sensitivity, and better stretchability of wearable electronics. Mass production, minimization and easy integration are also critical for the commercialization of wearable devices.  
[PERSON] has proposed the structure of the review and wrote the manuscript; [PERSON] and [PERSON] finished the manuscript together.  
This research was funded by the Programs for Beijing Science and Technology Leading Talent (Grant no. Z161100004916168), and the Fundamental Research Funds for the Central Universities (No. 06500100), and the \"Ten thousand plan\"--National High-level personnel of special support program, China.  
The authors declare no conflict of interest.