A fire-resisting enclosure/cabinet comprising an open-box like structure forming a body (11) to which is hinged a door (12). Both the body and the door are made up of an outer sheet steel skin (13) which has its one 'open' face closed by a liner (16;22). For the body, the liner (16) defines the inside of the body of the cabinet, whilst for the door the liner (22) defines the rear surface of the door of the cabinet. For both the body and the door thermally insulating material (30; 36; 42) is disposed in the space between the outer skin and the liner, with phase-change material (32) between the liner and the thermally insulating material and with fire-resistant concrete between the outer skin and the thermally insulating material. Engaging surfaces of the door and body respectively are formed by the material of the liner, i.e. polymeric material, thereby forming a near-hermetic seal therebetween in the event of fire.