by means of an actuator 14 for example an electromagnet for this purpose either said abutments pass through the fastenings 9 10 so that the electromagnet 14 can engage directly or the abutments 13 are themselves permanent magnets which when the outer electromagnets 14 are activated are repelled and are thus pressed inward in the form of instance a sealing diaphragm 15 is required the latter must be gastight so that the vacuum in the interspace 6 and inside the perforation 7 is maintained the abutments 13 co operate on both sides with supporting faces 12 which are formed as conical faces on the two outlet edges of the perforation 7 to form a coupling means in fig1 the abutments do not bear against the supporting faces 12 the inner container is connected to the outer container 1 only by means of the tension or compression struts 11 this first position corresponds to the standstill of the motor vehicle during which normally no vibrations of any kind occur the tension or compression struts 11 can thus be designed to be very lightweight and with a very small cross section so that they form only minimal heat bridges in the extracted detail a the abutment 13 bears against the supporting face 12 with the sealing diaphragm 15 being interposed in this second position the inner container 2 is firmly connected free of play to the outer container 1 the inner container is.