Thermal insulation of external walls is one of the most important topics in the design and making of buildings. Internal comfort and energy savings largely depend from the efficiency of the insulation. The proposed article analyzes and presents the evolution of thermal insulators in the building industry, from their first applications, to the most innovative systems currently present on the market, describing how social, political and economic changes have influenced the tendencies of research and production and showing how actual demands of sustainability and energy saving have lead to the introduction of high-performance materials and components in the construction industry.