The security document has a substrate (1) that comprises at least a first and a second substrate layer (7, 8) arranged on opposite sides of an intermediate layer (10). In a first region (5) of the document, the first and second substrate layers (7, 8) are connected to each other via the intermediate layer (10). Gaps or openings (11) in the intermediate layer (10) form a second region (6) or cavity where the first and second substrates (7, 8) are not connected. The security of the document can e.g. be improved by providing suitable patterns (14, 15) (for eg moire-effects by deforming, bending or compressing the substrate layers) or by embedding loose particles or a foil in the second region (6).