The glass transition temperature (Tg) of wool and its dependence on water contact is reinvestigated using differential scanning calorimetry (DSC). Previous studies with DSC have not accounted for the influence of thermal history, which may introduce a large variability in Tg measurements. Because of the Tg of wool is an important parameter affecting textile performance and properties, it needs to be clearly defined. When the finite volume of the water-impenetrable phase is taken into account, an important correction of the Fox equation is obtained, describing the dependence of Tg on water contact. On melting of the water-impenetrable crystalline regions, a reduction in the temperature range of the glass transition is apparent, suggesting that the crystalline regions behave in a manner analogous to filler particles in rubber. The ration of the change in heat capacity at the glass transition, before and after melting, may provide a way to estimate the crystalline weight fraction in native wool