Abstract: A freight container (1) has a frame to which a bottom (2), a roof (3), and sides (5-7) are attached, one side having a door opening closeable by a folding door (12) made of flexible, fire resistant material. The door (12) is supported from runners (13) moveable along a rail (14) combined with a top member (9) of a frame delimiting the door opening. A gap (15) is formed between the top frame member (9) and the top of the door (12) in its closed condition. The top member (9) is provided with a depending support (16) having a surface facing the inside of the door (12) and having attached thereto a strip of heat intumescent material (20). A flow passage (18) is formed between the strip (20) and the door (12) for gasses attempting to escape from the container through the gap (15) in a fire inside the container. The heat intumescent material (20) is arranged to swell and close the flow passage (18) when subjected to hot gasses from the fire inside the container.