An algorithm describing occupant clothing changes in response to thermal comfort was incorporated into a computer model for predicting the thermal conditions and resulting energy consumption of an office space. This model was used to investigate the effect of different levels of clothing flexibility on thermal comfort and energy consumption. Clothing flexibility was a very effective way of maintaining thermal comfort, and more effective than any fixed clothing ensemble. As clothing flexibility increased, a higher cooling set point and a lower heating set point could be adopted without affecting thermal comfort, but realising significant energy savings. The results illustrate the effect that consideration of occupant behaviour can have on simulation output, suggesting that recommendations for building operation based on the assumption of passive occupants may be sub-optimal. Crown in right of Canada