An approach called “COOL BIZ," which suggests raising the preset air-conditioning temperature to 28°C in summer as well as wearing lighter business clothes, has been promoted since 2005 for the possible reduction of the energy consumption in Japan. The objective of this study is to investigate the actual condition of workers' clothes in an office in which the air conditioner temperature has been set at 28°C in summer. Questionnaire results about clothes during the COOL BIZ period showed that the average value of basic thermal insulation of clothing (Icl) was 0.54clo for males and 0.52clo for females. The modal class of Icl for males in this study was lower than that from previous research in the 1970's. Most office workers answered that their thermal environment should be improved and that they used fans to alleviate their heat stress. Seventy-two percent of the respondents felt that the quality of their office environment lowered their work performance. When an effort is made to conserve energy, worker' performance should be taken into account.
