The invention is directed to a method and a system for using a thermal measurement method to determine the gas pressure in a vacuum element or in an evacuated body having an envelope and comprising on its exterior a flap delimited by two film faces that are joined together in the region of the free edge of the flap; the system according to the invention is characterized, on the one hand, by the fact that the space between the two film faces of the flap communicates with the space inside the envelope of the vacuum element and is at least partially filled with an open-pored, thin material layer, and, on the other hand, by a device for measuring the gas-pressure-dependent heat exchange coefficient of the flap at the location of the material layer; the invention also relates to the manner of operation of this measuring device.