Graphene-based nanocomposites have been shown to significantly enhance thermal conductivity as thermal interface materials (TIMs). An optimized mixture of graphene and multilayer graphene (MLG), produced via high-yield liquid-phase exfoliation, achieves a record 2300% increase in thermal conductivity (K) in a polymer matrix at 10 vol.% filler loading. This enhancement is attributed to a combination of high concentration of single- and bilayer graphene flakes and large, thick MLG flakes. The thermal conductivity of a commercial thermal grease was increased from ~5.8 W/mK to 14 W/mK at 2% loading, maintaining mechanical properties. Modeling suggests that graphene-MLG nanocomposites outperform carbon nanotubes (CNTs) and metal nanoparticles due to graphene's high aspect ratio and low Kapitza resistance at the graphene-matrix interface. The study demonstrates that a small addition of graphene-MLG (f~2%) can significantly improve the thermal conductivity of commercial thermal greases. Experiments and simulations show that more efficient TIMs can reduce thermal resistance between surfaces, lowering temperatures in integrated circuits (ICs). Achieving a 10-20 times increase in TIM thermal conductivity compared to the matrix would revolutionize electronics and renewable energy. TIMs fill surface gaps and are characterized by R_TIM = BLT/K + R_C1 + R_C2. They must be mechanically stable, non-toxic, low-cost, and have high K and low viscosity. Commercial TIMs have R_TIM ~3-10×10^-6 K m²/W. CNTs, though highly conductive, suffer from poor thermal coupling and high Kapitza resistance. Graphene and MLG, with high intrinsic thermal conductivity and low Kapitza resistance, offer superior performance. Graphene-MLG nanocomposites were synthesized using surfactant-stabilized dispersions and optimized sonication and centrifugation parameters. The resulting nanocomposites showed high thermal conductivity, with K reaching ~5.1 W/mK at 10% loading. The TCE was ~2300%, much higher than traditional fillers. The study also shows that graphene-MLG composites can achieve K ~14 W/mK in commercial thermal greases with only 2% loading. Theoretical models, including the Maxwell-Garnett effective medium approximation, support the high TCE of graphene-MLG composites. The study highlights the importance of graphene's geometry, low Kapitza resistance, and optimal filler mix for high TCE. The results demonstrate that graphene-MLG nanocomposites are promising next-generation TIMs with high thermal conductivity, low electrical conductivity, and excellent mechanical properties. The findings suggest that graphene-based TIMs can significantly improve thermal management in electronics and renewable energy systems.Graphene-based nanocomposites have been shown to significantly enhance thermal conductivity as thermal interface materials (TIMs). An optimized mixture of graphene and multilayer graphene (MLG), produced via high-yield liquid-phase exfoliation, achieves a record 2300% increase in thermal conductivity (K) in a polymer matrix at 10 vol.% filler loading. This enhancement is attributed to a combination of high concentration of single- and bilayer graphene flakes and large, thick MLG flakes. The thermal conductivity of a commercial thermal grease was increased from ~5.8 W/mK to 14 W/mK at 2% loading, maintaining mechanical properties. Modeling suggests that graphene-MLG nanocomposites outperform carbon nanotubes (CNTs) and metal nanoparticles due to graphene's high aspect ratio and low Kapitza resistance at the graphene-matrix interface. The study demonstrates that a small addition of graphene-MLG (f~2%) can significantly improve the thermal conductivity of commercial thermal greases. Experiments and simulations show that more efficient TIMs can reduce thermal resistance between surfaces, lowering temperatures in integrated circuits (ICs). Achieving a 10-20 times increase in TIM thermal conductivity compared to the matrix would revolutionize electronics and renewable energy. TIMs fill surface gaps and are characterized by R_TIM = BLT/K + R_C1 + R_C2. They must be mechanically stable, non-toxic, low-cost, and have high K and low viscosity. Commercial TIMs have R_TIM ~3-10×10^-6 K m²/W. CNTs, though highly conductive, suffer from poor thermal coupling and high Kapitza resistance. Graphene and MLG, with high intrinsic thermal conductivity and low Kapitza resistance, offer superior performance. Graphene-MLG nanocomposites were synthesized using surfactant-stabilized dispersions and optimized sonication and centrifugation parameters. The resulting nanocomposites showed high thermal conductivity, with K reaching ~5.1 W/mK at 10% loading. The TCE was ~2300%, much higher than traditional fillers. The study also shows that graphene-MLG composites can achieve K ~14 W/mK in commercial thermal greases with only 2% loading. Theoretical models, including the Maxwell-Garnett effective medium approximation, support the high TCE of graphene-MLG composites. The study highlights the importance of graphene's geometry, low Kapitza resistance, and optimal filler mix for high TCE. The results demonstrate that graphene-MLG nanocomposites are promising next-generation TIMs with high thermal conductivity, low electrical conductivity, and excellent mechanical properties. The findings suggest that graphene-based TIMs can significantly improve thermal management in electronics and renewable energy systems.