This study investigates the effects of curing temperature on the thermal conductivity of cross-linked high-density polyethylene (XL-HDPE). The specific objective is to evaluate the effect of cross-linking with peroxides and the addition of antioxidants on the thermal conductivity the material before and after vacuum degassing at curing temperatures of 180°C, 190°C, and 200°C. High-density polyethylene (HDPE) is used as the polymer matrix with di-cumyl peroxide (DCP) as the crosslinking agent, and Irganox 1010 (IX-1010) is added to mitigate the degradation of free radicals during the curing process. XL-HDPE samples are prepared through a melt mixing process followed by hot-pressing to ensure the homogeneous distribution of crosslinking agents and antioxidants. The thermal conductivity of XL-HDPE is measured by comparing the thermal conductivities of XL-HDPE with and without antioxidants before and after vacuum degassing. With the addition of 0.20 parts per hundred resin (phr) of antioxidants in the crosslinking process of HDPE with 1.01 phr of DCP significantly reduces the thermal degradation of HDPE, resulting in a higher thermal conductivity especially at 200°C which experiences the highest increase in thermal conductivity of 8.33% compared to that without antioxidants prior to vacuum degassing. Practically, this study offers a manufacturing protocol to enhance the intrinsic thermal conductivity of HDPE without conductive fillers. This particularly vital for thermal management systems in the nuclear, aerospace, and space industries, where materials must withstand vacuum environments and dissipate heat efficiently. © 2026 Wiley Periodicals LLC.