Ultralow thermal conductivity of nanoparticle packed bed

We show that thermal conductivity of packed bed of alumina nanoparticles can be as low as 0.035W?mK which is only 35% higher than the thermal conductivity of air and is smaller than the recently reported lowest thermal conductivity of solids using disordered layered WeS2. These findings show a promising approach for making low-cost and ultralow thermal conductivity thermal insulation materials with high density and good sustainability at high pressures.