This paper defines a “human requirements envelope” for the thermal environment in vehicles, based on a method of assessment that has evolved during 5 years of vehicle R&D with a thermal manikin. VOLTMAN is a clothed, full-size, articulated model of a seated adult male. The entire skin surface is divided into 19 sections, each section heated subcutaneously under multi-channel process-computer control to maintain a skin temperature distribution typical for sedentary comfort (Mean value 32.8°C). Total heat loss and the distribution of heat flow over the body surface can be accurately measured on-line. Total heat loss affects driver performance, and therefore safety, while sectional heat loss determines comfort, draught sensation, and the risk of cold-related muscular injury. On the basis of systematic comparisons of human and manikin response to the complex thermal environment in vehicles, standard procedures have been defined for assessing whether a given vehicle fulfils human requirements under specified operating conditions. Sectional heat loss is expressed as Equivalent Homogenous Temperature (EHT) by means of reference exposures to a homogenous, draught-free environment. Thermal asymmetry in a vehicle is then represented as an “EHT-Profile”. Ideal Profiles (IP) for vehicle occupants, differing between winter and summer, are proposed, and acceptable EHT-ranges for each body section (<20% dissatisfied), defined as Vehicle Comfort Regions (VCR) on the profile diagram. A figure of merit for a vehicle climate is available: SDIP, the standard deviation of an EHT-Profile from the relevant IP, the IP being positioned for this purpose so as to result in the same total heat loss as for the measured profile.