Abstract: It is already known that heat insulating elements, e.g. in refrigerators, may be more efficient if they are sealingly encapsulated and subjected to a high vacuum. Based on theoretical considerations in connection with foam having small cells it has been relevant to use a vacuum of the magnitude of 0.001 mbar and hermetical sealing of the elements. According to the invention it has been found that practically well usable results are achievable at much higher pressures, viz. in a range about 1 mbar, which is much easier to produce. Consequently, a further simplification can be obtained by renouncing the hermetical sealing and relying on an only "almost tight" sealing, combined with the use of an operationally active vacuum pump provided in each apparatus unit.