“As most collectors are aware, a dust jacket in fine condition can greatly enhance the value of a book.”
Andrea Koczela (2015), Books tell you why.
It seems that these first came into existence around the middle of the nineteenth century, when the production of books was industrialized. Their purpose was to protect the valuable binding, at least for a time. Different from the cover, the jacket bore the title of the book and often further particulars also on the front panel. At times this was merely a straightforward copy of the title page with, perhaps, a border drawn around it. In the first decades of our century it was the cover itself that, to its detriment, became the carrier of a marketing tool: the title.
A book jacket is a kind of poster. It is designed not only to draw attention but also to protect the cover from light, dirt and abrasions until the book is safely in the hands of the buyer. Publishers make book jackets not so much to present the buyer with a protective cover for his book but to guard themselves and the bookseller against loss. Carefully made books should never be distributed without a jacket, be it ever so humble.
(…) A jacket is not an actual part of the book. The essential portion is the inner book, the block of pages. Even cover and endpapers, strictly speaking, are false parts, temporary only, because they will be discarded when the book is re-bound. The only valid book title sits inside the book, on the title page. Whatever is written on the jacket does not matter to the bibliographer; therefore it is not necessary and indeed an error to so much as mention the existence of a jacket. Like an advertising leaflet that has been inserted between the pages, a jacket is merely a floating addendum. For the same reason, pictures on the jacket or protective cover and those glued to the cardboard slip case should neither be assumed to be nor described as genuine components of the book. If they constitute an essential part, they should be added to the inner book, perhaps in the form of a frontispiece. Pictures on the wrapper or the cover are soon damaged.
Tschichold, Jan. 1991. The Form of the Book:
Essays on the Morality of Good Design : 161.
“Dust jackets were first used during the 19th century. During this period books were expensive items bound in fine materials such as leather or silk and displayed as desirable objects. Such examples of craftsmanship needed protection during their journey from the bookseller or binder to the library, and so the dust jacket came about. Initially these were just plain paper wrappers and once a book had been unwrapped its dust jacket was thrown away.”
in Victoria and Albert Museu (s.d.).
Disponível em: http://www.vam.ac.uk/content/articles/h/history-of-the-dust-jacket/
SOBRECAPA – Folha impressa, de papel forte ou de qualquer outro material, que envolve a capa de um livro quando da sua publicação. Capa de protecção. Cobrecapa. Sobrecoberta. Guarda-pó. Jaqueta. Dust jacket. Camisa. Não faz parte dele e é facilmente separável; muito usada nos últimos anos, o seu emprego generalizou-se tanto para livros brochados como para livros encadernados; tem a vantagem de tornar o livro mais atraente servindo, deste modo, fins de propaganda comercial, além de que o resguarda e protege, especialmente se se trata de uma edição de luxo.
Just as the external elevations of a Modernist building express the structure and internal planning, the cover should reflect the typographic structure of the text pages. Yet the cover and the text pages have distinct functions. The cover is to the text as clothes are to the body.
The cover of a paperback not only takes the place of the binding of a conventional book: like the book jacket, it has an earlier life, used by publishers’ salesmen as a marketing aid before the book is produced.
HOLLIS, Richard (1934). Writings about graphic design, Occasional Papers : 30
CAPA – Parte exterior de um documento, seja de que matéria for, destinada a protegê-lo; pode conter o título da obra, o nome do autor e do editor, a data, etc. Cobertura. Página de cobertura • Folha de papel sobre a qual se imprime o título da obra e que a envolve, enquanto brochura; nos livros modernos é usualmente feita em papel colorido, com desenhos mais ou menos vivos e atraentes.
CAPEAR – Revestir com capa. Encapar.