Raising Acoustic, Mechanical, and Thermal Properties of Flexible Polyurethane Foams via Hazelnut Shell and Hemp Fiber Hybrid Fillers

The growing demand for sustainable materials drives the integration of natural fillers into flexible polyurethane foams. This study explores a novel hybrid filler system using hazelnut shell powder (HSP) and industrial hemp fibers to enhance acoustic, mechanical, and thermal properties while reducing petroleum‐based components. Flexible foams were produced with filler loadings of 1.5%, 3%, and 6% for each material. Samples were analyzed using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), compression testing, and acoustic measurements. Results show that foams with 3% hazelnut and 3% hemp achieved an 8% increase in compressive strength at a density of 168 kg/m 3 . Acoustic tests revealed that 1.5% blends improved sound transmission loss at 250 Hz by 4.13 dB, while 3% blends enhanced performance at 6300 Hz by 13%. Thermal stability showed marginal improvement with filler addition. These findings demonstrate that combining hazelnut shell powder and hemp fibers can significantly enhance foam properties while reducing reliance on petroleum‐derived components. The dual‐filler strategy offers a novel route toward more sustainable polyurethane foams.