Today, besides standard insulation products reflective thermal insulations can be purchased on the market. This may for example be a combination of closed air layers with several layers of metallized foil. Dealers of reflective insulation often claim that the thermal conductivity of reflective insulation reaches values lower than 0,01 W/(m‧K). One dealer introduces this fact to consumers in another form: three centimeters of reflective insulation are equal to twenty centimeters of mineral wool. However, are such properties physically possible?