## 3 Results and Discussion
### Test Results of the \"TFK\" Sample  
The load/deflection curves of the TFK sample are shown in Figure 5. At the beginning of the research, a force of 1000 N caused the maximum deflection of 142.43 mm (TFK 100), while at the end, it was 147.13 mm (TFK 82,500). Both curves exhibited a nonlinear increase in load with deflection, indicating the elastic and nonlinear deformation properties of the mattresses. At lower loads and deflections  
Figure 5: Load/deflection curve for TFK sample after 100 and 82,500 cycles. (up to approximately 40 mm), the curves are relatively similar, indicating a comparable initial stiffness. As the load increased, the differences between the two curves became more apparent, with TFK 100 supporting a slightly higher load at the same deflection than TFK 82,500. TFK 100 exhibited a higher load support capability, particularly at deflections greater than 80 mm. The TFK 82,500 supports a slightly lower load at the same deflection, indicating that it may be softer or more compliant. The mattress height of the unloaded surface (Figure 6) remained relatively constant, starting at 241 mm and ending at 236 mm, indicating a minimal change in the mattress thickness over the cycles. The mattress height exhibited minimal changes, indicating good structural integrity and resistance to permanent deformation. This consistency suggests that the materials, both springs and foam, maintained their shape and support during prolonged use. The hardness value (H) fluctuated slightly but generally decreased with an increase in the number of cycles. It starts at 5.86 N/mm and ends at 5.21 N/mm, with some variations between cycles. The hardness value exhibited some variability, with peaks at certain cycles (e.g., 4.91 at 15,000 cycles and 5.96 at 45,000 cycles). This variability may indicate the response of mattress materials (inner pocket springs and polyurethane foam) to cyclic loading and unloading. At 30,000 cycles (i.e., the end of the standardized procedure), the values of H and the Hs are 5.37 N/mm and 7.7, respectively. These values were also very close to the final values achieved by the mattress at 82,500. Similar to the case of PUR, this may indicate that 30,000 cycles are sufficient to assess the main characteristics of the mattress. The test for the TFK sample was stopped after 82,500 cycles due to the broken pocket spring (Figure 7a,b). The surface of the mattress above the broken spring exhibited damage to the fabric, indicating changes in its interior (Figure 7c). However, the location of the break was sufficiently far from the loading location of the loading pad; therefore, the break did not affect the measurement results. Figure 6: Hardness value (H) and firmness rating (Hs) for sample TFK. The firmness rating (Hs) remained relatively stable, starting at 7.3 and ending at 7.1, with minor fluctuations throughout the cycles. The firmness rating remained more stable than the hardness value, which indicates that the subjective firmness (perceived comfort) of the mattress did not change significantly over the cycles. Minor fluctuations in Hs suggest that while the material properties might be altered slightly, the overall user experience in terms of firmness remains consistent. The mattress height at a 50 N load remained relatively stable, starting at 227.3 mm and ending at 224.4 mm (Figure 8). Minor fluctuations in height were observed, but overall, the mattress maintained its height well under a 50 N load. This stability is crucial to ensure consistent support and comfort over the lifespan of a mattress. In the final cycles, the height was 224.4 mm, indicating a height loss of the TFK mattress of 2.86 mm. Figure 8: Mattress height, height changes and height loss for sample TFK. The framed bar represents the total height loss. Figure 7: (**a**) Core of the mattress at the point of breakage (broken spring is circled), (**b**) broken and whole spring, (**c**) location of damage on mattress surface. Initially, the mattress height increases, reaching a maximum change of 4.56 mm at 60,000 cycles.