The thermal acceptability of males and females wearing uniform summer clothing ensembles of 0.54 clo or 0.95 clo units and exposed to ASHRAE summer comfort envelope temperatures of 73°FET* (22.8°CET*), 76°FET* (24.4°CET*), and 79°F (26.1°CET*) was investigated. Variables were tested for a 90-minute period using 108 female and 108 male college students exposed under stable and controlled conditions. Thermal responses were measured using a thermal sensation ballot for the body as a whole and for the face, hands, and feet; a thermal comfort ballot; and the weighted mean skin temperature. In general, results validated both the 0.5 clo value specified in ASHRAE Standard 55-1981 for summer comfort envelope conditions and the 0.95 clo value determined using the Thermal Comfort Threshold formula for optimal satisfaction at 73°FET* (22.8°CET*).