Thermal insulating plasters and renders are becoming a popular solution for the energy retrofit of existing and historic buildings because of their suitability/compatibility with the existing masonry supports. However, as for most of the insulating products, the actual performance of these materials might significantly differ from the one determined with simplified methods (EN ISO 6946 standard) that are commonly adopted by the designers. In this study, an overview of the latest Authors researches that involve three different thermal insulating plasters, containing respectively perlite, vegetal and aerogel aggregates, are presented. The developed plasters were characterized in the laboratory and successively applied in three demonstration buildings. From the in-field thermal monitoring activities, all the analysed thermal insulating plasters showed a decrease in the thermal performance between 25 and 30% if compared to the laboratory measurements.