Fick's laws, stating that diffusion rate is proportional to the concentration gradient, have traditionally been used to describe the drying of wood. The author contends that they have been used inappropriately, since according to Fick's laws the rate varies as the concentration gradient of diffusing molecules, whereas many wood scientists use the concentration gradient of non-diffusing molecules —the bound water. When the temperature-dependent component of the diffusion coefficient is combined with the concentration gradient of diffusing molecules, the resulting driving force is proportional to the vapour pressure, and the diffusion coefficient is independent of temperature.