Abstract: Shipping system for temperature-sensitive materials. In one embodiment, the shipping system may include an insulated container. The insulated container may include a frame surrounding a payload space, the frame including a door providing access to the payload space. The shipping system may additionally include a door brace assembly. The door brace assembly may be mounted within the payload space just inside the door and may include a door plug configured to substantially close the payload space. The door brace assembly may additionally include a door brace mounted within the door plug. The door brace may be transformable between a retracted state and an expanded state. When in its retracted state, the door brace assembly may be loaded into or removed from the insulated container. When in its expanded state, the door brace assembly engages the four corners of the frame just inside the door to keep the frame square.