Abstract Studies on the influence of radiotherapy on the structure, thermal properties, and thermo-oxidative decomposition of breast silicone implants were conducted. Additionally, the potential use of breast silicone implant waste as a component in layered composites was investigated. ATR-FTIR, DSC, and TG/DTG/FTIR analyses confirmed that radiation does not affect the structure, thermal properties, or oxidative decomposition behavior of the shell and gel layers of breast silicone implants. The conducted tests demonstrated the successful fabrication of composite materials using a PUM matrix and breast silicone implant waste. The presence of the PUM matrix in the manufactured composites influenced the crystallization and melting behavior of the silicone phase. Moreover, the incorporation of a silicone implant waste layer into the composites increased their thermal stability while decreasing the glass transition temperature, storage modulus and hardness compared to neat PUM. The type of implant waste layer used (shell or gel) in the preparation of the PUM composites did not significantly affect the melting and glass transition temperatures, thermal stability, or oxidative decomposition behavior of the newly developed materials. As demonstrated, new layered composite materials based on silicone implant waste (shell and gel), with properties valuable for practical applications, were successfully developed. Keywords: breast silicone implants; post-mastectomy radiotherapy; reuse of breast implants; TG/DTG/FTIR