ASHRAE Standard 55-1981and Chapter 8 of ASHRAEHandbook--1981 Fundamentalsspecify the environmental conditions that are thermally acceptable to most people at different levels of clothing insulation and metabolic activity. It is necessary for users of these documents to determine what types of clothing provide different amounts of insulation. The purpose of this study was (1) to expand the current data base of insulation (clo) values for garments and clothing ensembles commonly worn in indoor environments and (2) to develop and compare different methods for estimating clothing insulation. The clo values of 115 different garments and 60 representative ensembles were measured using a standing, electrically heated manikin in a climate-controlled chamber. Regression analysis was used to relate a number of variables to garment and ensemble insulation. A new computer model, which calculates local and total body heat loss (or clothing insulation), was developed also. The relative accuracy of the predictive equations and model was determined and discussed.Units: SI