Ett isoleringsmaterials teoretiska isoleringsförmåga undersöks med tester som utförs i laboratoriemiljö, vilket skiljer sig avsevärt från verkliga förhållanden. Syftet med detta examensarbete är att forska om vilket U-värde isoleringsmaterial har under verkliga förhållanden. Två frågeställningar har formulerats: Vilket behov finns det av att testa isoleringsmaterials verkliga isoleringsförmåga? Vilken metod är mer lämplig för att undersöka isoleringsmaterials verkliga isoleringsförmåga, att studera uppvärmningsbehov hos befintliga byggnader eller hos experimentmoduler? Studien har påvisat ett teoretiskt behov av att studera verklig isoleringsförmåga. En metod för jämförelse av befintliga byggnaders verkliga uppvärmningsbehov har tagits fram och ett experimentförslag med testmodul har designats. Slutsatsen är att det föreligger ett teoretiskt behov av att studera isoleringsmaterials verkliga isoleringsförmåga, samt att studie av uppvärmningsbehovet hos experimentmoduler är den mest lämpliga metoden för att undersöka verklig isoleringsförmåga. / In recent decades, the increasing requirements of energy use in buildings have resulted in a demand for more well-insulated and airtight structures.The theoretical insulation capacity of an insulating material is determined during tests performed in a laboratory environment. The problem is that these conditions differ significantly from real conditions.The purpose of this thesis is to investigate the U-value of insulating materials in real conditions. The thesis does not include execution ofexperiments. Furthermore, the study is limited to Swedish conditions and two insulation materials: polyurethane and mineral wool. For this purpose,two problem statements have been formulated: • What is the need for testing insulating material’s true insulating abilities? • Which method is more suitable for examining insulating material's true insulating ability, studying the heating needs of existing buildings or experiment modules? The study was based on literature studies where the following information and data were studied: • Previous studies on the insulating ability of insulating materials • Existing methods for comparing the actual heating needs of existing buildings • Calculation methods for theoretical heating needs, structural strength and building-related physics • Swedish climate conditions and Swedish requirements for buildings The study has shown that previous research on true insulating ability is lacking and that previous comparisons of insulating ability do not take actual conditions into account. Furthermore, the study has found an absence of existing methods for comparing the actual insulation capacity of existing buildings. Verified methods for assessing the actual energy use of buildings, in combination with the energy calculation method, have been used to create a method for comparing the actual heating needs of existing buildings. Finally, an experimental proposal with a test module has been designed. The design includes drawings, design requirements and expected energy requirements for two different insulation materials.The conclusion is that there is a theoretical need to study the actual insulating ability of insulating materials, and that studying the heating requirements of experimental modules is the most appropriate method for investigating real insulating ability.