A roller door system (100) particularly for opening and closing a doorway (120) defined in the wall of a lightweight structure (110) such as a marquee, hangar, field hospital, emergency shelter and the like. The door system comprises a rollable door (150) secured, in use, along one edge of the doorway (152); a roller (140) for rolling and unrolling the rollable door about the roller; an opening mechanism and a closing mechanism for controlling the deployment of the rollable door by translating the roller across the doorway; and reusable sealing means (135, 136, 155, 156) for sealing between the lateral margins of the rollable door and the doorway; characterized in that the rollable door comprises a plurality of collapsible hoses (165, 166) connected to a pressurized fluid power system (160, 161, 163) such that in use a positive pressure applied to the fluid power system causes the rollable door to unroll from the roller and controls the deployment of the rollable door.