Characterization of foam shells by optical interferometric techniques is limited by scattering caused by the foam structure. Such scattering reduces the transmitted light intensity and fringe contrast. Additionally, fringe position is not a sensitive detector of shell defects. Because of the low density of the foam, relatively large shell non-concentricity or local defects cause only slight changes in the fringe position. We have used model calculations to estimate foam parameters required to enable adequate foam shell characterization for a baseline shell.