## 3 Results and Discussion
### Resistance to Multiple Washing Cycles  
The tests have demonstrated that subjecting the insert to multiple cycles of water washing at a low temperature (30 \({}^{\circ}\)C) did not cause a significant change in electrical power and resistance (Table 7). After 25 washing cycles, the power of the insert decreased slightly by 0.13 W. In contrast, its electrical resistance increased from 6.86 \(\Omega\) for a new insert to \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number of**} & \multirow{2}{*}{**Applied**} & \multicolumn{2}{c}{**Power, W**} & \multicolumn{2}{c}{**Electrical Resistance, \(\Omega\)**} \\ \cline{3-5}  & & **Variant A** & **Variant B** & **Variant A** & **Variant B** \\ \hline
0 & & 2.09 & 2.15 & 6.91 & 6.86 \\
500 & & 2.08 & 2.11 & 6.89 & 6.98 \\
1000 & 4 V & 2.08 & 2.04 & 6.89 & 6.98 \\
5000 & & 2.09 & 2.06 & 6.91 & 7.07 \\
9000 & & 2.08 & 2.07 & 6.89 & 7.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Electrical properties of heating inserts (variant A and B) after multiple bending cycles. Figure 9: Thermal resistance test results for systems of materials incorporating heating inserts A and B depending on the number of bending and twisting cycles. 7.21 \(\Omega\) for an insert after 25 washing cycles. The above differences are not significant. The developed heating inserts were found to retain their electrical properties after repeated washing cycles. As in the case of determining resistance to multiple bending and twisting cycles, organoleptic observations of heating inserts after multiple washing cycles did not show any damage to the knitted fabric or heating thread (Figure 10). Research concerning the washability of e-textiles and heating elements has been very limited. As indicated by [PERSON] et al. [35], the current standards in the field of textiles lack an adequate consideration of integrated electrically conductive and electronic components of e-textiles. There is a need to develop a future standard to provide a range of washing programs for materials incorporating different kinds of electrical devices. [PERSON] et al. [36] found in their research that the resulting damage was quite limited if the tested conductive textiles were only exposed to a single cleaning factor (a detergent or mechanical agitation). Significant losses in conductivity did not occur until multiple factors acted and interacted at the same time. Therefore, it is very important to develop a correct estimation of washability under real usage conditions for materials with conductive elements. Studies of the thermal resistance of heating inserts in a system with underwater showed that the repeated washing of the inserts did not cause a significant change in their thermal resistance. In both insert variants--without an openwork knitted fabric (A) and with such a fabric protecting the conductive thread (B)--thermal resistance was at a similar level before the first washing (0 cycles) and after 25 washing cycles. The difference amounted to approx. 0.15 m\({}^{2}\)K/W (Figure 11), which attests to the durability of the inserts and their resistance to the water washing process. It was found that the thermal resistance of both insert variants that were turned off during the test was lower by approx. 0.05 m\({}^{2}\)K/W as compared to the inserts that were turned on in the heating operating mode (Figure 11). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Number of Washing Cycles** & **Applied Voltage, V** & **Power, W** & **Electrical Resistance, \(\Omega\)** \\ \hline
0 & & 2.15 & 6.86 \\
10 & & 2.06 & 7.06 \\
15 & 4 V & 2.02 & 7.19 \\
20 & & 2.01 & 7.17 \\
25 & & 2.02 & 7.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Electrical properties of the heating insert (variant B) after multiple washings. Figure 10: Photographs of heating inserts after 25 cycles of washing—inner surface of variant A (**a**) and inner surface of variant B (**b**). In the case of heating insert A, it was noticed that washing resulted in the heating thread being locally pulled up to form loops.