A stripped book is a mass market paperback that has been stripped of its cover in order to be pulped and recycled as a result of lack of sales. The covers are returned to the publisher as evidence that the books have been destroyed and the books are discarded or recycled into paper or cardboard products. However, some stripped books end up back on the marketplace, and are sold at places like flea markets. As a result, beginning in the 1980s, most publishers of mass market paperbacks insert a warning on the copyright page, often containing the note:
If you purchased this book without a cover you should be aware that this book is stolen property. It was reported as "unsold and destroyed" to the publisher and neither the author nor the publisher has received any payment for this "stripped book."
A few hardcover titles also carry the above warning, but hardcover books are generally not stripped, as the publisher expects them to be returned intact so they can be sold as remaindered books.
A more specialized use of the term "pulping" is to refer to the system of destroying unsold books (usually but not always mass market paperbacks). If a book is not selling well, the publisher may not only allow it to go out of print by ceasing to print more copies, but (for tax purposes) destroy any copies they cannot sell by the end of the fiscal year. Bookstores strip the front covers from paperbacks that do not sell, and return them to the publisher as evidence they have been destroyed rather than sold. The books are then burned or recycled into paper or cardboard products.
This system of pulping paperback books evolved from the rise of the mass market distribution system following World War II when paper was cheaper than the cost of transport. Coverless paperbacks are often found for sale in thrift stores, charity libraries (in hospitals, for instance), flea markets, and the like; sometimes even in used bookstores. In the 1990s, publishers began an information campaign to alert book buyers to the fact that these books have been reported as destroyed, to mixed results.
The practice of pulping, as opposed to remaindering, has the long-term effect of diminishing the number of copies of a given print run or edition and of making the surviving copies more valuable in the book collecting market.