Method for manufacturing a heat-insulating closed structure

A method for the manufacture of a heat-insulating closed structure, which comprises the steps of:

• forming a composite membrane having an inner membrane, which is formed of a gas-impervious and transparent substance having small holes at appropriate intervals thereof, disposed a distance from the inside of an outer membrane, which is formed of a gas impervious substance, through the medium of spacers;
• fastening said composite membrane to a heat-insulating floor member in an edge-to-edge manner;
• applying pressure to the space enclosed by said composite membrane and said heat-insulating floor member for thereby inflating the composite membrane and allowing it to stand up on its own;
• injecting a foaming dope into the cavity defined between the inner membrane and the outer membrane from the interior of said structure and through said small holes of said inner membrane;
• and whereby the use of said transparent inner membrane facilitates the monitoring of said injection of said dope from the interior of said structure.