The thermal insulation (clo) values of clothing ensembles commonly worn by men and women in indoor environments were measured using an electrically heated manikin. The same designs, construction methods, and support materials were used to make a set of winter and summer garments, differing only in fabric type. Garments such as a suit jacket, vest, sweater, and tie were systematically added to basic trouser ensembles and skirt ensembles to study the effect of garment layering and closure. Results indicated that adding or removing certain garments and changing how they are worn on the body affect the level of clothing insulation. Winter ensembles were significantly warmer than comparable summer ensembles, but the insulation provided by most summer ensembles was higher than that indicated byASHRAE Standard 55-1981for typical summer attire. In addition, a high correlation between ensemb1e weight and clo value was found.