# Static Factors in Sitting Comfort: Seat Foam Properties, Temperature, and Contact Pressure
## 2 Influence Parameters
### Interface Temperature Influence on Perceived Comfort  
Thermal comfort is an important parameter to consider when assessing passengers' comfort. Multiple authors stated that there is evidence that the heat exchange at the seat-user interface influences perceived comfort [39; 40; 41; 42]. The heat exchanges between the human body and its surroundings in a railway vehicle can be compared to that in a car seat. Those heat exchanges are influenced by four mechanisms of heat transference: convective, radiative, conductive, and evaporative, and can be calculated as follows Equation (3):  
\[Q=Q_{cv}+Q_{cd}+Q_{r}+E_{sk} \tag{3}\]  
where \(Q\) represents the total heat exchanges, \(Q_{cv}\) is the convective heat transfer, \(Q_{cd}\) relates to the conductive heat transfer, and \(E_{sk}\) means the evaporative heat transfer. In a closed environment, as in the case of rail vehicles, the human body exchanges more heat with surroundings by radiation and conduction. Additionally, conduction heat exchanges assume a critical significance as a considerable portion of the body surface area is in contact with the seat [43]. This way, the seat cover is also a determinant factor in thermal comfort.  
When the contact pressure is associated with thermal accumulation, discomfort and harmful consequences may be raised by the users [44]. Current investigations focus more on analysing pressure-distribution comfort than the seat-passenger interface temperature [45]. This way, a research gap was identified.  
Infrared thermography is a technique capable of being applied to investigate thermal exchanges. Thermographic cameras operate following the principles of [PERSON], Wien, Planck, and Kirchhoff laws [46]. The Planck law states that all bodies above an absolute zero temperature (-273.15 \({}^{\circ}\)C, i.e., 0 K) are constituted by small particles in continuous motion in a random direction that emit electromagnetic radiation [47; 48]. Therefore, thermographic cameras detect the infrared radiation emitted by a body and convert it into a thermal image. In conclusion, this non-destructive and non-invasive technique allows the mapping of materials to locate temperature variations [49]. Thus, this methodology can help investigate the existence of microclimates at the seat cushion interaction [7].  
[PERSON] et al. [47] employed infrared thermography to evaluate the thermal response of seat cushions and backtests of eight different chairs (with varying designs and materials). Results demonstrated a similar behavior of leather and fabric covers (main interest cover materials of the present section), as they reported final temperatures around 30 \({}^{\circ}\)C, promoting a temperature increase of approximately 6-7 \({}^{\circ}\)C.  
[PERSON] et al. [44] reported that foam thickness interferes with thermal conductivity. The temperature at the body-seat contact surface increases as the foam thickness increases. By applying an infrared thermographic camera on four different wheelchair cushions, [PERSON] et al. [50] concluded that lower temperatures at the seat-user interface promote higher comfort levels.  
[PERSON] and [PERSON] [51] investigated the influence of both seating temperature and interface pressure on sitting discomfort levels. Contrary to what was reported by other authors, results suggested that high temperatures were not necessarily associated with discomfort, and low interface pressures may not be linked to comfort. These contradictory results highlighted the need to perform more experimental campaigns regarding static sitting comfort and the parameters capable of affecting it.