The use of large volume sealed stainless steel capsules has allowed the measurement of a transition temperature in wool at a range of moisture contents using differential scanning calorimetry. Aged wool showed an endothermic peak that disappeared after cooling from above the transition temperature, but was restored with subsequent ageing at ambient temperature. Similar behavior is characteristic of amorphous polymers annealed below their glass transition temperature. Moisture appeared to act as a plasticizer in wool and lowered the transition temperature. At moisture contents of 22% the transition temperature approached 35 degrees C, and the application of this result to the formation of severe wrinkles in wool garments during wear is discussed.