# Static Factors in Sitting Comfort: Seat Foam Properties, Temperature, and Contact Pressure
## 3 Experimental Campaign
### Experiment 1: Mechanical Properties Assessment
To understand the effect of the seat cover, cushions were compressed with and without cover, and the increasing hardness percentage was calculated. Table 3 exhibits the 25% _ILD_ cushion hardness with and without seat cover and the increase %. By analysing the results of Table 3, it can be concluded that current foams have a higher hardness than older ones. Moreover, hardness increases as the foam thickness rises, which is demonstrated by comfort foams that show a higher 25% ILD hardness than the standard ones, in agreement with [PERSON] [26]. Additionally, the seat cover highly influences the system's (foam and cover) hardness. While the leather cover promoted a maximum increase of 28%, the fabric cover corresponded to a 44% hardness increase. It should be highlighted that if a cover is stretchable and loosely connected to the foam, the mechanical properties of the seat are more dependent on the cover, as the foam can freely deform. In opposition, a stiff cover tightly attached to the foam may limit the foam deformation and, consequently, influence the seat performance [18]. Additionally, an extra experiment assessed the foam and cover capacity for absorbing energy. That consisted of releasing a ball (52 mm diameter and mass of 127 g) and measuring its initial and bump heights (Figure 5). That was constituted by the seat (with and without cover) (1), a motion sensor CBR 2 (Texas Instruments) (2) [60] capable of measuring and recording distance, velocity, and acceleration, connected with a computer (3) and the ball (4). The calculation of energy absorption %, follows Equation (4):  
\[\%\ E_{abs}=\frac{\
u_{2}}{\
u_{1}}\times 100=\left(\frac{h_{2}}{h_{1}} \right)^{1/2}\times 100 \tag{4}\]  
where \(v_{1}\) and \(h_{1}\) are corresponding to the ball's initial speed and height and \(v_{2}\) and \(h_{2}\) represent the ball's rebound speed and height. It was assumed that the ball acts as a rigid body. This way, the ball did not lose energy, but the seat cushion suffered deformation due to the collision [61]. Measurements were recorded at a 50 Hz sample frequency. Experiments were run five times for each cushion with and without the seat cover. Table 4 presents the experiments' mean energy absorption percentage. The cover increases the energy absorption percentage, especially the leather cover. At the current AP seats, energy absorption increases by 14% and 10%, respectively, for the comfort and standard seats. That absorption percentage increase is less noticed for the older seats, as the fabric cover only increased 2% and 11% of the energy absorption for the comfort and standard cushions, respectively. This way, based on the hardness increase and \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Seat Cushion**} & **25\% ILD** & **25\% ILD** & \multirow{2}{*}{**Increasing \%**} \\  & **Foam Hardness (N)** & & **Foam+Cover Hardness (N)** & \\ \hline Current comfort seat & 288 & 360 & 26 \\ \hline Current standard seat & 250 & 320 & 28 \\ \hline Older comfort seat & 271 & 354 & 44 \\ \hline Older standard seat & 167 & 240 & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Foam hardness results with and without a seat cover. the energy absorption percentage, the leather cover appears to be more suitable for seating applications. Nevertheless, more experiments need to be performed to properly evaluate the cover influence.