Abstract: A spatially expandable hollow body construction is provided which is adapted to be filled by a fluid to provide expansion thereof. The construction includes a first fluid-inflatable hollow body including an outer skin, means for enabling automatic filling of the main hollow body by the sucking in of a fluid such as air when the skin of the main body is expanded and for preventing the escape of the fluid from the main body through the filling means, and a second, fluid inflatable hollow body connected to the first hollow body and arranged such that inflation of the second hollow body causes expansion of the skin of the first hollow body and consequent filling of the first hollow body by the sucking in of the ambient air. The filling means may comprise a simple non-return valve or a valve device which selectively provides shut-off of the inlet for the main body and the inlet for the second body.