## 3 Results and Discussion
### Specific Heat Capacity, Thermal Diffusivity, and Thermal Conductivity  
The specific heat capacity values in the solid state of the neat PCMs and impregnated EG are reported in Figure 8.  
The specific heat capacity strongly increases with temperature, confirming well-known trends already encountered for other organic PCMs [45], and an incipient variation before the main melting point was observed, with a direct consequence on the \(c_{p}\) evaluation, as observable in other studies on PCM's thermophysical properties [46; 47; 48]. Note that for RT35 and RT35/EG14, the specific heat capacity evaluation is not possible above 25 \({}^{\circ}\)C because the phase transition has already started; hence, the specific heat capacity cannot be defined. The same consideration is valid for RT44 and RT44/EG14 above 30 \({}^{\circ}\)C. The trend for each PCM is confirmed also in the presence of EG, which decreases the specific heat capacity in all of the compositions due to the lower specific heat capacity of EG [39; 49], particularly for MPA. On the contrary, RT44 is not drastically affected by the EG addition. Moreover, an uncertainty of \(\pm\)4% in the heat flux, due to DSC calibration, must be taken into consideration [50]. The mean values and standard deviation of the three tested specimens for each sample are reported in the results to simplify the visualization. However, the trends are not affected by this issue, because the same calibration was adopted for all the specimens. The EG's beneficial effect on enhancing the thermal diffusivity can be seen in Figure 9a, and in Figure 9b, the thermal diffusivity values are normalized with respect to those of the neat PCMs to appreciate the improvement inferred by EG. From Figure 9a, an opposite trend with respect to the specific heat capacity can be noticed, with a decrease in thermal diffusivity when the temperature increases. Also, in this case, the most pronounced decreasing trend with temperature is presented by RT35/EG14, which, in this case, possesses the lowest values among the three compositions. From Figure 9b, it is possible to appreciate how the highest thermal diffusivity increase, thanks to the EG matrix, is exploited by MPA (more than 20 times), followed by RT44 (around 13 times), and finally RT35 (8 times). Figure 8: Specific heat capacity in the solid state from 20 \({}^{\circ}\)C to 35 \({}^{\circ}\)C.  
The thermal conductivity values, calculated using Equation (3), are reported in Figure 10.  
Although the specific heat capacity and thermal diffusivity are directly measured independently, the indirectly evaluated thermal conductivity trends are quite constant with temperature; hence, a sort of compensation between thermal diffusivity decrease and specific heat capacity increase occurs. This constancy of the thermal conductivity with temperature is in agreement with many other studies, but, rarely, it is correlated to two opposite trends of specific heat capacity and thermal diffusivity. The highest value is 5.95 \(\pm\) 0.07 W/m\(\cdot\)K, reached at 25 \({}^{\circ}\)C by RT44/EG14, which corresponds to an enhancement of 16 times with respect to the neat PCM. Lower values are obtained for MPA/EG14 (4.73 \(\pm\) 0.01 W/m\(\cdot\)K at 30 \({}^{\circ}\)C) and RT35/EG14 (4.03 \(\pm\) 0.15 W/m\(\cdot\)K at 25 \({}^{\circ}\)C). The high uncertainty in the determination of the specific heat capacity of RT35/EG14 propagates to the thermal conductivity, leading to standard deviation values much higher with respect to RT44/EG14 and MPA/EG14. Figure 10: Thermal conductivity assuming constant bulk density in the solid state in the range 20–35 \({}^{\circ}\)C (**a**) and thermal conductivity enhancement after EG addition (**b**). Figure 9: Thermal diffusivity in the solid state from 20 \({}^{\circ}\)C to 35 \({}^{\circ}\)C (**a**) and thermal diffusivity enhancement after EG addition (**b**).