Abstract: A liner is described for containers such as fluid tanks, gasoline tanks, and tank trucks and railroad tank cars. The liner is a thick flexible membrane styled, shaped and arranged to fit closely within the inside and against the inside wall of the container, and the liner has a plurality of flexible tubular ribs therein. The tubular ribs are filled with a material such as foamed polyurethane or other fluid under pressure, and when the tubes are filled they hold the liner against the interior wall of the container, even though the container is empty.