Some manufacturers of infrared reflective insulation products claim that their relatively thin products feature the same high thermal performance as 20 cm mineral wool. They maintain that their products cannot be described through conventional methods of building physics, their thermal efficiency can only be determined by in situ tests. Two identical buildings, which allow comparative measurements of different roof systems under identical boundary conditions, are located at an outdoor testing facility in Southern Germany. In one of the attics a conventional roof system using mineral wool has been installed. Infrared reflective insulation has been applied to the other roof system. The products have been chosen to have the same thermal efficiency as specified by their manufacturers. Extensive comparative measurements have been carried out. Conventional laboratory measurements of the insulation products have been done and compared to the results of the in situ measurements. Furthermore, the examinations have been completed with dynamic calculations. The result is that the examined roof system with infrared reflective insulation shows typical insulation characteristics yet with lower thermal resistance. The values of the common laboratory measurements have been confirmed through the results of the in situ measurements. Thus, the infrared reflective products (Fig. 1) can be described using traditional building physics. (C) 2012 Elsevier B.V. All rights reserved.