<p>Effective thermal management is critical for advanced electronic devices, yet conventional polymer-based thermal interface materials (TIMs) often exhibit low thermal conductivity, poor filler dispersion, and high interfacial resistance. This study addresses these limitations by enhancing filler–matrix interactions and exploiting synergistic effects between dual-dimensional carbon nanofillers. Graphene (GPs) and multiwalled carbon nanotubes (MWCNTs) were non-covalently surface modified using phenyl glycidyl ether (PGE) via ultrasonication in THF, improving dispersion and compatibility with room temperature vulcanizing silicone rubber (RTV SR). The surface-functionalized fillers (PGE@GP, PGE@MWCNT) were characterized using FTIR, Raman spectroscopy, FESEM, and TGA to confirm successful modification. Composite films were fabricated by incorporating PGE-modified fillers into RTV SR at three different hybrid ratios (PGE@GP:PGE@MWCNT = 9:1, 8:2, and 7:3) with a total filler content of 10 wt%. The composite with a 9:1 ratio achieved the highest thermal conductivity of 0.459 ± 0.001 Wm⁻¹&#xa0;K⁻¹, representing a 129.5% enhancement over pure RTV SR. The observed 48.06% synergistic improvement highlights the effectiveness of combining dual-dimensional fillers. Additionally, the composite retained electrical insulation, a critical property for TIM applications. Application tests using a 1 W LED bulb demonstrated the composite’s ability to dissipate heat efficiently, confirming its potential as a high performance, electrically insulating thermal interface material for modern electronic systems.</p> Graphical abstract <p></p>