Large aperture parabolic reflectors are needed for space applications in different wave-length ranges including the millimetric and submillimetric ones where a high accuracy is required for the reflecting surfaces. We propose to get more accurate surfaces by replacing the preformed flexible membranes presently scheduled in the inflatable technology, by elastic disks whose thickness variation along a radius is calculated in order to obtain, after inflation, parabolic caps. As an illustration of the method, polyester and polyimide membranes are investigated. Provide a variable thickness from the center to the edge is obtainable, large aperture parabolic cap may reasonably be considered as feasible. The surface accuracy depends mainly on the elastic properties of the material and the thickness control.