tIn Italy, historic buildings constitute 20% of the built environment. Although historic buildings are usuallyexcluded from the obligation of adopting specific energy standard, energy related aspects should benevertheless faced and managed in order to exploit the building “usability” potential, to attain indoorenvironmental quality and energy efficiency conditions. The energy refurbishment of this kind of buildingis, however, a very complex matter that leads to a number of question concerning buildings conservationand valorisation aspects. A non-invasive technique, that is, the application of thermal plaster to theinternal side of a building envelope, has been investigated in this paper. Thanks to its relatively easyinstallation and reversibility, thermal insulating plaster seems to represent a very interesting solution asit is able to offer a good compromise between energy and conservation aspects.The aim of this work is to present a thermal, vegetal based, insulating plaster, which has recently beendeveloped within a research project, and to investigate its potential to reduce the heat flux exchangedthrough the vertical envelope of historic buildings, by means of measurements carried out in both thelaboratory and in the field, for a real case application.