The paper deals with the idea that one of the inner thermal insulation layers of garment may be replaced by expanding air chambers in the form of an expanding thermal insert which is inflated with air causing chamber thickness and thermal insulation properties to change. The chambers are controllable so that thermal insulation properties can be changed, and by connecting with an appropriate control architecture an article of clothing can be designed which can independently monitor changes in its environment and change its thermal insulation properties in accordance with changes in its external and internal environment. In this way it acquires characteristics of intelligent clothing. The paper presents idea concepts, development, structural architecture and general characteristics of two generations of intelligent clothing with adaptive thermal insulation properties. The expanding thermal inserts are situated between the outer shell and the lining and are the key element of this kind of new clothing. In the first generation of intelligent clothing the expanding inserts were designed in combination with three horizontal chambers that can be sealed in three horizontal layers whereby it is possible to make six adaptable discontinuous levels of thermal insulation. In the second generation ribbed expandable chambers were used. Their thickness is continuously changeable according to pressure change in the chambers whereby the value of thermal insulation of the chambers can be continuously adapted. The functioning of this clothing is based on the integration of sensors for internal and external temperature and air pressure in the chambers, on a microcontroller with regulation software and actuators to control the expanding insert. When wearing this kind of clothing the microcontroller system monitors changes in ambient temperature and clothing microclimate depending on the wearer’s physical activity, compares them with the achieved thermal protection and makes autonomous decisions on the required increase or decrease in thermal protection. Since this clothing follows changes in its internal and external environment, estimates the real and necessary state, makes decisions and independently performs the adaptation of thermal insulation to the level ensuring constant thermal comfort, it can be claimed that such a garment has basic attributes of intelligent clothing. The paper describes the functioning of two types of thermal insulation chambers, sensor system used, micropneumatic components, microcomputer system, flow chart of the algorithm of intelligent behavior, complete built-in architecture of all technical subsystems, features of the first and second generation and observed good and bad points of the conceptual approach to the development of intelligent clothing with adaptive thermal insulation properties.