This study investigates the potential of composite allotrope boron nitride nanobarbs (BNNBs) as nanoparticles for enhancing the thermal conductivity of nanofluids based on mixtures of ethylene glycol and propylene glycol with water. BNNBs are allotrope composites composed of boron nitride nanotube cores with walls decorated with attached hexagonal boron nitride crystals, creating a jagged morphology that facilitates the formation of a connected network and contributes to the enhancement of thermal conductivity in nanofluids. BNNBs exhibit high thermal conductivity due to efficient phonon transfer and they are electrical insulators owing to their wide bandgap. The effect of BNNB concentration in carrier fluids on nanofluid thermal conductivity was investigated by introducing BNNBs into ethylene glycol-water and propylene glycol-water mixtures at 0-10 wt%. The results showed that BNNBs enhanced thermal conductivity of carrier fluids up to 45%, and the enhancement was proportional to the concentration of BNNBs in the carrier fluid. The study also investigated the dispersion stability of BNNBs in different solvents using Hansen Solubility Parameters, revealing that propylene glycol mixtures demonstrated better long-term stability compared to ethylene glycol mixtures. The findings suggest that BNNBs have great potential for use as thermally conductive nanoparticles in nanofluids for various heat transfer applications. Future research should focus on enhancing the dispersion stability of BNNB nanofluids and exploring the influence of BNNB morphology on the thermal conductivity and other thermophysical properties of nanofluids.