An apparatus and a method for adapting a prefabricated item of footwear that is formed, at least in part, of hard thermoplastic material, to a user's foot and/or leg. A pressure-exerting element is provided that substantially encloses the item of footwear and that has an accommodating space into which the item of footwear can be placed. The accommodating space is bounded, at least in part, by a deformable material which forms an inner layer of the pressure-exerting element, which contains a cavity and has an inlet opening provided for the introduction of a pressure application fluid. The pressure-exerting element is formed with a portion into which the pressure application fluid cannot enter.