The comparison of the results presented in Fig. 6 suggested that the WVTR is sensitive to environmental temperature and RH, as well as the coating weight. High temperature and high humidity conditions promote the transferring of water vapor, thus leading to much higher WVTR values at 37.8◦C and 90%RH compared to those at 23◦C and 50%RH. Both the coating weight and the testing conditions played important roles in WVTR results. Fig. 6 shows that, when the coating weight was at the low level of 10 g/m2, the coating layer hardly showed the positive effect on lowering the WVTR of coated paper when tested at 37.8◦C and 90%RH; where as the WVTR at 23◦C and 50%RH decreased dramatically. The higher the coating weight, the further lower WVTR values were achieved. The main reason is that the higher coating weight of the composites provided higher chances covering porous structure on the surface of the handsheets.