There are various commercial techniques in use today. Commercially produced books tend to be of one of five categories; hardcover, paperback, cardboard article, a sewn book, or comb-bound.
A hardcover or hardbound book has rigid covers and is stitched in the spine. Looking from the top of the spine, the book can be seen to consist of a number of signatures bound together. When the book is opened in the middle of a signature, the binding threads are visible. The signatures in modern hardcover books are typically octavo, though they may also be folio, quarto, or 16mo. Usually large and heavy books are sometimes bound with wire or cable. The covers of modern hardback books are of thick cardboard. Until the mid 20th century mass produced books were covered in cloth, but from that period beyond most publishers adopted clothette. Clothette is a kind of textured paper that vaguely resembles cloth but is easily differentiated on close inspection.
A paperback or soft cover book consists of a number of signatures or individual leaves between covers of much heavier paper, glued together at the spine with a strong flexible glue. This is sometimes called perfect binding. Mass market paperbacks and pulp paperbacks are small, cheaply made and often fall apart after much handling or in several years. Trade paperbacks are more sturdily made, usually larger, and more expensive.
A cardboard article looks like a hardbound book at first sight, but it is really a paperback with hard covers. It is not as durable as a real hardbound. Often the binding will fall apart after a little use. Many books that are sold as hardcover are actually made this way.
A sewn book is constructed in the same way as a hardbound book, except that it lacks the hard covers. The binding is as durable as that of a hardbound book.
The rise of desktop publishing has brought comb-bound binding into the commercial market. A comb-bound book is made of individual sheets, each with a line of slits punched near the bound edge. A curled plastic comb is fed through the slits to hold the sheets together. Comb binding allows a book to be disassembled and reassembled by hand without damage.