The adaptive thermal comfort model links indoor comfort temperatures to prevailing weather outdoors, shifting them higher in warm weather and lower in cool weather. Adaptive comfort engineering standards hold the potential to conserve energy, but for them to work effectively it is essential that building occupants are free to adapt themselves, primarily through clothing adjustment, to the variable indoor climatic regimes prevailing inside such buildings. This paper examines clothing behaviour and its relationship with thermal environments in 2 different indoor settings located in Sydney, Australia. The first was in a suburban shopping mall, and the second in a callcentre office. The company operating the call-centre had a strict business attire dress-code in force Mondays through Thursdays, but on Fridays employees were free to wear casual clothes. Indoor temperatures throughout both studies were relatively static despite significant weather and seasonal trends operating in the outdoor atmospheric environment. Clothing insulation values of garments worn inside the shopping mall showed significant day-to-day variation, with the standard deviation representing about 34% of the mean clo (1 clo = 0.155 m² K W⁻¹) value during the study period. Typical shopping mall clo values during summer were more than 0.6 clo lighter than those worn in winter, and a regression model of daily average clo on daily mean outdoor temperature explained 52% of the variance in clo values. Clothing insulation levels worn on Œstrict business attire¹ days in the call-centre study were relatively static, regardless of weather or season, and they showed only a weak statistical relationship with indoor temperature variations (R² = 20%). In contrast, the much more variable clo values worn by the office workers on Œcasual¹ days, showed a significant correlation with outdoor temperatures (R² = 44%). Based on these relationships, an adaptive comfort model for use in hybrid ventilation buildings is proposed.