The purpose of this study was to investigate the effects of two kinds of underwear material on subjects exercising and resting in an ambient temperature of $20^{circ}C$, a relative humidity of 60% and an air velocity of 0.13m $see^{-1}$. Two kinds of underwear ensemble were tested, differing in their hygroscopic properties: 100% wool (W) with higher moisture regain and 100% cotton (C) with lower moisture regain. Five young females served as subjects. The experiments comprised two repeated periods of 15 min exercise on a treadmill with a speed of 6km $h^{-1}$ followed by 10 min rest. The main results were as follows: 1) Mean skin temperature was significantly higher in W than in C throughout the whole experimental period (p<0.05). 2) The temperature and humidity of the microclimate between the skin and underwear provided by the first layer of clothing was higher in W than in C (p<0.1 and p<0.05, for temperature and humidity, respectively). 3) Heart rate was significantly higher in W than in C (p<0.05). 4) Subjects felt warmer during the second exercise session when wearing wool rather than cotton (p<0.05), and they also reported more increased wetness during the second exercise and rest periods in W than in C (p<0.05). These results suggest that underwear made of wool with higher moisture regain might not act as effectively as cotton to transfer exercise-induced heat from the body to the surrounding air when light exercise is taken in a thermally-neutral environment.