## 4 Conclusions  
The preliminary results showed that the PUR sample demonstrated good durability and stable mechanical performance after the initial break-in period (Figures 2 and 3), making it suitable for long-term applications in which repeated loading is expected. The sample experienced an initial phase of significant compression, followed by a stabilization period in which the height changes were minimal (Figure 4). After the initial phase, the properties of the foam stabilized, showing consistent hardness and firmness values until the end at 90,000 cycles. The material showed good durability with minor fluctuations in height change, suggesting slight recovery and minor compression.  
From the TFK sample, users can expect consistent firmness and support from the beginning and throughout their usage. The sample featuring inner pocket springs and polyurethane foam exhibited strong performance characteristics and durability (Figures 5 and 6). Over an extensive testing period, the mattress showed only a slight decrease in the hardness value, indicative of minor material softening. However, the firmness rating remained largely stable, ensuring consistent support and comfort for the users. The mattress height changed minimally (Figure 8), demonstrating the structural integrity and resistance to deformation of the product up to 82,500 cycles when spring breakage occurred. These results highlight the ability of the mattress to provide long-term reliability and support on sleeping surfaces.  
The proposed hypothesis was confirmed, but not to the extent and intensity as expected. Namely, changes in the hardness, firmness and height loss of the mattress occurred during the experiment (i.e., use of mattress), but they were not expressed to the extent that a decrease in the quality of the mattress is observed; on the contrary, the samples proved to be very stable. Indirectly, these limited results indicate that the impact of changes on sleep quality can be negligible. The cause of such results surely lies in the insufficient number of tested samples and their composition.  
Although this was not the aim of the research, the results indicated that 30,000 cycles can be sufficient to assess mattress quality; however, it should be kept in mind that this research included only one sample of each type of mattress, which is certainly not enough to draw conclusions.  
The limitations of this study are the small sample size and lack of variability in mattress types.  
The results of this preliminary study show possible expectations that have yet to be confirmed by testing a larger number of samples with more diversity in types of mattresses. It is necessary to include mattresses with innersprings (Bonnell, pocket), foams (polyfoams, viscoelastic, gel-infused), latex and hybrid (e.g., visco-foam, innerspring and latex), or special poly-foams and latex intended for use in \"medical\" or \"therapeutic\" products--all in combination with different top layer types and thicknesses. In addition, to better understand the broader context of sleep comfort, future research should include comparisons of the results of subjective assessments supported by body pressure distributions.  
Conceptualization, Z.V. and N.K.; methodology, Z.V.; validation, Z.V., N.K., and D.D.; formal analysis, N.K.; investigation, N.K.; resources, Z.V.; data curation, Z.V.; writing--original draft preparation, Z.V. and N.K.; writing--review and editing, Z.V. and D.D.; visualization, Z.V. and N.K.; supervision, Z.V. and D.D.; funding acquisition, Z.V. and D.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
All relevant data are within the paper. The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors express their gratitude to [PERSON] and [PERSON], from the Laboratory for Furniture (LIN), for their assistance during the preparation of the experimental tests.  
The authors declare no conflicts of interest.