This study investigates the degradation of polyamide 12 (PA12) powder used in Selective Laser Sintering (SLS) technology, focusing on how repeated usage affects powder performance and the quality of printed parts. Multiple printing cycles were carried out using an EOS P396 SLS printer, including pure virgin powder, reused powder, and a 50:50 mixture of new and used powder. The research evaluated powder behavior during the printing process, mechanical properties through tensile testing, and visual surface quality of printed samples. Results showed significant issues in the first and second cycles, such as uneven powder spreading, sintering outside target areas, and part deformation. Tensile tests revealed the lowest strength in parts from the second cycle, while the test cycle with mixed powder showed the highest average stress values and the best visual quality. The findings mostly confirm EOS suggestions, that powder degradation significantly affects mechanical performance and print quality, and that proper mixing and moisture control can mitigate some negative effects. This research highlights the importance of powder management for maintaining part integrity and optimizing the sustainability of SLS production.