The hygroscopicity of wood after polyethylene glycol (PEG) impregnation and/or heat treatment was investigated by testing the water uptake, equilibrium moisture content (EMC) at various relative humidity levels, and contact angle of the poplar wood surface. The results showed that: (1) At the first moment, the heat treatment at temperatures lower than 160 ℃ did not reduce the water uptake because of the lowered wettability of wood after those treatments. Afterwards, all the heat treatments showed positive effect on reducing the water uptake until they reached the same maximum after 48 d in this study. (2) PEG increased the water uptake at beginning but significantly decreased the maximum water uptake, and the PEG-heat treated showed additive effect by showing further lower maximum water uptake. (3) The molecular weight of PEG showed slight influence on both water uptake and moisture adsorption. (4) The heat treatment at temperatures below 160 ℃ showed little influence on equilibrium moisture content (EMC), but significantly decreased the EMC above 160 ℃. The combination of PEG-heat treatment produced inconsistent results at different relative humidity levels. After PEG 1000 impregnation, the EMCs were a little higher than those without PEG for both unheated and heat treated samples at high relative humidity conditions (75%). However, at low relative humidity conditions (11, 33, 57%), the EMCs of PEG treated wood are all lower than those without PEG impregnation. The reason needs to be further discussed.

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