## 2 Materials and Methods  
### Tested Object  
The technology of flexible thermoelectric modules is currently under development [14]. In the course of the market analysis performed, only one manufacturer offering commercial flexible thermoelectric modules was identified: the TEGway company ([[http://tegway.co](http://tegway.co)]([http://tegway.co](http://tegway.co)) accessed on 24 August 2021). TEGway modules are made of many small-area elementary cells based on bismuth and tellurium (BiTe). These elementary cells are connected electrically and mechanically by a filling made of flexible plastic. This results in their parallel connection in the thermal domain and their series connection in the electrical domain. The FTE1-01 module (Figure 1) was selected for the laboratory tests, with dimensions of 68 mm \(\times\) 85 mm \(\times\) 2.3 mm, a fill factor (ratio of the active area to the total TEC area) of 17%, a number of elementary cells of 169, a maximum heat flux of 76.5 W, and a maximum temperature difference of 60.8 \({}^{\circ}\)C. The decisive choice criteria were the fill factor and the size of the active surface as compared to other modules offered [15].  
The key to ensuring effective cooling by a TEC module is the appropriate selection of a heat sink receiving heat from the hot side of the TEC. For the selected flexible thermoelectric modules FTE1-01, it was decided to use three heat sink variants: two dedicated for these specific modules--a metal and a polymer one--and another polymer one, designed within the research project.  
The metal heat sink (Figure 2) has a weight of 67.54 g and dimensions of 89 mm \(\times\) 68 mm \(\times\) 15 mm. It is stiff, but due to its thin base, it can be bent in one direction, and after removing the force, the element does not return to its original form. The heatsink height of 15 mm makes its practical use in cooling garments limited; however, the decision was made to use it in tests for comparison purposes.  
The TEGway polymer heat sink (Figure 3) is flexible in all directions. Its weight is much lower than that of a metal heat sink, amounting to approx. 7.58 g. The dimensions of this heat sink are 117 mm \(\times\) 95 mm \(\times\) 1.50 mm when dry. This element uses the evaporation effect to receive heat from a TEC. Before using this element, the manufacturer recommends soaking it in water for a few minutes and then squeezing it lightly so that water does not flow out of it during use. When wet, the heat sink absorbs moisture, increasing its weight and thickness.  
Figure 1: View of the FTE1-01 module (TEGway).  
Figure 2: Metal TEGway heat sink.  
In order to carry out the laboratory tests, an attempt was also made to develop an own heat sink using a non-woven fabric with superabsorbents (SAPs). This heat sink was made of melt-blown non-woven polypropylene fibers with 14% superabsorbent powder with an area weight of 84 g/m\({}^{2}\) (Figure 4). For its production, 5 layers of the above-mentioned non-woven fabric were used, which were inserted between the Pontetorto polyester knit (backsheet) and the Toray polyamide fabric (topsheets). The resulting heat sink has dimensions of 117 mm \(\times\) 95 mm \(\times\) 6 mm, and its dry weight is 7.66 g. The area is therefore the same as for the TEGway polymer heat sink, while the thickness is determined by the number of layers of melt-blown non-woven fabric used, which in turn was selected so that the total dry weight was similar to the weight of the TEGway polymer heat sink.  
The variants selected for the laboratory tests are listed in Table 1.