A covering an architectural opening including a support tube and a panel operably connected to the support tube and configured to be wound around the support tube. The panel includes a support sheet and at least one cell operably connected to the support sheet. The at least one cell includes a vane material operably connected to a first side of the support sheet and a cell support member operably connected to the vane material and configured to support the vane material at a distance away from the support sheet when the panel is in an extended position with respect to the support tube.