The equilibrium moisture content in wood depends not only on the current relative humidity in ambient air, but also on the history of relative humidity variations. This hysteresis dependence of sorption in wood implies that in the worst case the moisture content for a given relative humidity may deviate by 30–35%. While researchers seem to have reached a general agreement on the hypothesis for the sorption hysteresis phenomenon, only a few models describing the phenomenon are available. Current models such as the independent domain model have numerical deficiencies and drawbacks. This paper presents a new hysteresis model, which mathematically resolves in closed-form expressions, with the current relative humidity and moisture content as the only input parameters. Furthermore, the model has the advantage of being applicable to different sorption isotherms, i.e., different species and different temperatures. These features make the model relatively easy to implement into a numerical method such as the finite element method.