The device has thick planks made of foam and connected together by paper sheets in a correlative manner, where designs such as drawings or captions e.g. title of a book, are printed on the paper sheets. The paper sheets are glued on faces of the planks. A reinforcing back part (4) is fixed on a back side of the book, and is provided with two outer paper layers (6, 7) and an intermediate sheet layer (5). One of the paper layers constitutes an outer cover of the reinforcing back part.
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