Abstract Sawdust, a natural and renewable material from wood processing, has become more and more widely reused in biomass-based thermal insulating material preparation. However, there is still a lack of biomass-based thermal insulating material, which should possess a characteristic of easily preparation but high thermal insulation performance. Herein, we developed an eco-friendly thermal insulation material by firstly pre-pressing sawdust powder into packed bed and then carbonizing the sawdust bed into porous carbon bed. The influences of the bed structure, environmental temperatures and humidity on the thermal conductivity of the prepared beds were firstly investigated. Results turn out that the carbonized pine sawdust packed (CPP) bed could have a low thermal conductivity of about 0.062 W m - 1 K - 1 . A high intrinsic porosity of sawdust particle, high porosity of bed, and spherical shape of pores in the CPPs are preferred for reducing the thermal conductivity. Moreover, the prepared CPPs not only possess hydrophobicity but also show excellent reusability and structural stability. The thermal conductivity of CPPs can be fully recovered without obvious structure collapse, if dried again after placed under a relative humidity of 60% for more than 24 hours. Importantly, the CPPs has excellent flame-retardant and smoke-free property because of the carbonization treatment in the preparation, and it can self-extinguish within 6 seconds in the vertical burning test. This work provides a facile and sustainable strategy to manufacture thermal insulation material from recycling waste bioresources, which has potential for future energy saving in buildings.