An implantable fluid device comprises a flexible fluid chamber capable of being in an inflated state and a deflated state. The chamber has a first end, a second end, and a central longitudinal axis from the first end to the second end. The chamber also has, in cross section when deflated, a plurality of alternating protrusions and intermediate portions about the central longitudinal axis. When deflated, the protrusions have a selected height and the intermediate portions have a selected depth. When inflated, the protrusions have the selected height and the intermediate portions have a selected height.