This article focuses on aspects related to the physical and thermal parameters of so-called thermal-insulating paints. These materials and systems are used in two different situations: first, as agents reducing surface temperature due to solar radiation, and second, as so-called “thermal-insulating” coatings. The paper focuses on the second aspect of the applications described by the manufacturers and presents the results of the author’s laboratory tests (using an insulated heating box with two different heat sources) and field tests (in situ) on a building façade. The research methodology focuses on contact and thermal imaging measurements to assess the effectiveness and properties of reflective thermal-insulating paints, as well as analyzing their impact on the surface temperature and heat transfer coefficient of building envelopes. The conducted research showed that the use of reflective thermal-insulating paints does not significantly improve the thermal insulation of building envelopes. Measurements of the heat transfer coefficient showed a reduction of 1–7% compared to the reference wall tested. In situ measurements using temperature sensors and thermographic studies confirmed the insignificant impact of reflective thermal insulation paints on the thermal protection of external walls.