Leather is a niche material used for upholsteries, gloves, and garments due to its high durability, flexibility, and softness properties. The inclusion of nanoparticles in the leather matrix provides multifunctionality for high-performance applications. Herein, we synthesized hexagonal boron nitride (h-BN) nanoparticles via a single-step hydrothermal synthesis and treated the leather after dispersing in polyethylene glycol (PEG) to yield h-BN/PEG-treated leathers. Atomic force microscopy and high-resolution transmission electron microscopy analysis ascertained the particle size of 30–50 nm for as-synthesized h-BN nanoparticles. h-BN nanoparticles along with PEG were successfully incorporated into the leather matrix, and this was confirmed by surface and morphological studies using field emission scanning electron microscopy/energy-dispersive X-ray analysis and Fourier transformed infrared spectroscopy. Leathers treated with h-BN/PEG were studied for insulation against heat and cold, and the results displayed improved thermal insulation properties compared to the control leathers. The dynamic mechanical analysis of control and treated leathers demonstrated higher storage modulus, loss modulus, and tan δ values for h-BN/PEG-treated leathers, signifying an increased energy absorption and dissipation potential, which was further ascertained by the low-velocity drop-weight impact resistance test. Thus, the results of this study open up new prospects for h-BN/PEG-treated leathers in strategic applications demanding high thermal insulation and impact resistance properties.