A roller door (11) having a door panel which includes a plurality of horizontal slats (13). The horizontal slats are made from a closed cell polyethylene foam material. The horizontal slats are held together by one or more substantially vertical and flexible elongate members (15) which are connected at an upper end to an accumulation device, for example a drum. Each horizontal slat connects with the adjacent horizontal slats with a tongue and groove joint, the joint being configured to allow a small amount of pivoting to occur at the joints so that the door panel can be rolled onto the drum. Contact between adjacent horizontal slats comprises direct contact between the foamed plastics material of each adjacent horizontal slat.