A load port for loading wafers to and unloading wafers from a front opening unified pod (FOUP) includes a shield member that covers and provides a seal over an opening of the FOUP. The shield member includes a narrow wafer slot that is sized to allow a single wafer to be loaded to or unloaded from the FOUP but otherwise minimize loss of the purge environment within the FOUP. The shield member is movable so that the wafer slot may be moved vertically to provide a wafer transfer robot access to any desired wafer position within the FOUP. The shield member, for example, may be a flexible sheet that is held taut and is rolled onto and off of at least one roller to vertically position the wafer slot. The shield member may alternatively be one or more rigid members that slide on rails to vertically position the wafer slot.