Fire resistant door

A fire resistant door has a core 16 comprising magnesium oxide board and a cellulosic fibre material sheet, the core being surrounded by frame components 20 and covered on at least one side by a door skin 12, 14 which is attached to the frame components. The core 16 may further comprise cellulosic fibre material sheets 30a, 30b between which the magnesium oxide board 32 is sandwiched. These sheets may comprise depressions that accommodate inwardly moulded regions of the door skin. As an alternative to the magnesium oxide board, surfaces of the depressions and/or the moulded regions can be covered by an intumescent material. Fire resistant doors with thicknesses as little as 35mm may be manufactured.