A scalable high-porosity wood for sound absorption and thermal insulation

The search for more-sustainable materials has motivated research on lightweight, porous structures for thermal insulation and noise reduction, such as for construction and cold-chain transportation. Wood, known as one of the most renewable materials on Earth, has been widely and long used in construction for its high strength/weight ratio, wide abundance, low cost and relative sustainability. However, natural wood is much less effective at reducing noise or preventing heat loss than conventional petroleum- and mineral-based porous structures (for example, expanded polystyrene foam and mineral wool). Here we report the extraordinary noise-reduction and thermal-insulation capabilities of a scalable, high-porosity wood structure, ‘insulwood’, fabricated by removing lignin and hemicelluloses from natural wood using a rapid (~1 h) high-temperature process followed by low-cost ambient drying. Insulwood demonstrates a high porosity of ~0.93, a high noise-reduction coefficient of 0.37 at a frequency range of 250–3,000 Hz (for 10-mm-thick wood), a low radial thermal conductivity of 0.038 W m^–1 K^–1 and a high compressive strength of ~1.5 MPa at 60% strain. Furthermore, this new wood-based material can be rapidly processed into a vacuum insulation panel (~0.01 W m^–1 K^–1) for thermal insulation applications with limited space (for example, refrigerators, cold-chain transportation and older buildings). The material is unique in its combination of renewable source materials, high porosity, high sound absorption, low thermal conductivity and high mechanical robustness, as well as in its efficient, cost-effective and scalable manufacturing. These attributes make insulwood promising as a sustainable construction material for improved noise and thermal regulation.