## 3 Results and Discussion
### Test Results of the \"PUR\" Sample  
The load/deflection curves of the PUR samples are shown in Figure 2. At the beginning of the research, a force of 1000 N caused the maximum deflection of 107.79 mm (PUR 100), while at the end, it was 109.43 mm (PUR 90,000). The nearly identical shapes of the curves suggest similar load-bearing characteristics but with some offsets. The load/deflection curves for PUR 100 and PUR 90,000 show the typical behavior expected of polyurethane foam, with initial linear elasticity, a plateau for energy absorption, and a final steep densification phase. The primary distinction between the two types of curves lies in their initial stiffness and the slight variations in their load-bearing capacities. PUR 90,000 appears to have a slightly steeper initial slope than PUR 100, suggesting that PUR 90,000 may be slightly stiffer in this initial phase. After the initial 100 cycles, the height of the unloaded surface of the mattress with a PUR core was 192 mm (Figures 3 and 4). The height decreased slowly and slightly, reaching 186 mm by the 90,000 th cycle. The mattress height showed a consistent slightly downward trend, suggesting gradual compression over time. The initial hardness value (H) and firmness rating (Hs) of the mattress were 11.04 N/mm and 2.8, respectively (Figure 3). Between 100 and 7500 cycles, the largest changes in hardness and firmness occurred when the hardness value decreased by 28% to approximately 8 N/mm and the firmness rating increased by more than 50% at 4.3. After its initial drop, the hardness value stabilizes, fluctuating slightly between 7.53 N/mm and 9.03 N/mm to maintain a value of 8.60 N/mm at the end of the test. After 30,000 cycles, which represents the end of the test according to the standardized procedure, the value of H was 8.73 N/mm, and the value of Hs was 4. These values are very close to the final values achieved by this mattress at 90,000, which may indicate that testing the mattress for 30,000 cycles is sufficient to assess its quality. Figure 2: Load/deflection curve for PUR sample after 100 and 90,000 cycles. After 90,000 cycles, the test of the PUR sample was stopped owing to the stagnation of the firmness results in the last three measurements; however, there was no visible damage on the surface or inside the mattress. After reaching 4.3, the firmness rating stabilizes,  
Figure 4: Mattress height, height changes and height loss for sample PUR. The framed bar represents the total height loss. Figure 3: Hardness value (H) and firmness rating (Hs) for sample PUR. showing minimal fluctuation between 4.0 and 4.6 throughout the remaining cycles. The firmness rating did not show significant changes after the initial increase, indicating a stable firmness over time (Figure 3). To determine the height loss, mattress heights were measured under a load of 50 N. As shown in Figure 4, the initial height of the mattress was 178.4 mm, which decreased slightly over the cycles. This indicates gradual compression of the mattress material under repeated loading. By 90,000 cycles, the height was 174.6 mm, which means that the height loss of the PUR mattress was 3.79 mm. Observing height change relative to the initial measurement, there is a height change of 2.78 mm at 7500 cycles. The height change relative to the initial measurement increases progressively, peaking at 4.00 mm at 37,500 cycles. After 37,500 cycles, the height change decreases slightly, fluctuating between 3.28 mm and 3.79 mm. This indicates that the mattress experienced the most significant compression in the early cycles and stabilized afterward. The height changes relative to the previous measurement showed both positive and negative values, indicating minor fluctuations in height from one measurement to the next. Initial cycles of up to 7500 show a significant positive change (2.78 mm). Negative changes occur at 22,500 cycles (\(-\)0.51 mm) and at other intervals, suggesting a slight recovery or settling between measurements.