　　Paper is the base of all printing and binding, the canvas on which every image appears. The type of paper, its weight/thickness, coating(s), texture, grain direction, opacity, and color all should be carefully considered when planning a printed piece. Just as the image to be printed will affect the type of paper chosen, the bindery requirements of your job must also be taken into account.
　　Paper is made up of fibers. These fibers most often come from wood, but cotton, linen, and other materials are also used. Research continues into alternative sources of fiber for paper, including bamboo, hemp, and rice straw. Clay or other materials can also be added after the basic fiber base is laid down to create "coated" papers.
　　For the bookbinder, there are two main areas of concern with regard to paper: grain direction and coating. These two characteristics are important to us because of what we do to the paper. In the process of binding a single book, we squeeze your paper between knurled rollers, grab it with mechanical fingers or suction, mash it in a hydraulic press, heat it, wet it, and apply up to six different kinds of glue to it. Scoring, folding, sewing, gluing, and cutting are all influenced by the characteristics of the paper, sometimes radically. Grain direction and coating can be the difference between the bookbinder's efforts leading to skillful conversion of flat printed sheets into fine, long lasting books, or a wrinkled, cracked, mangled mess.
　　Grain
　　Grain is important both to the printer and the bookbinder. It is critical that your job be planned from the very beginning with grain direction in mind. This can affect not only the appearance and durability of your book, but also the sheet sizes available to you--and thus press size, yield, and cost.
　　When paper is manufactured commercially, the fibers in the pulp line up more or less in one direction. This is known as the grain direction of the paper. You can discern the grain direction of a piece of paper in several ways. Simply bending the sheet is usually indication enough--the paper is much harder to fold against (perpendicular to) the grain than with (parallel to) the grain. One surefire way to determine grain direction is to lay a small sheet of the stock gently onto the surface of a pan of water. This wets one side of the sheet, while the other side stays dry. The paper fibers will swell on the wet side and cause the sheet to curl up into a tube--the length of the tube is the grain direction. This simple test illustrates one reason why grain direction is so important to the bookbinder.
　　Grain and Glue
　　When we bind a hard cover, case bound book, water-based glue is used at several stages of production. When the endsheets are "tipped" on to the first and last signatures, a thin bead of glue is used. Also, when the book is "cased-in"--i.e. when the text is attached to the cover--the entire outside of each endsheet is coated with a thin film of glue. Naturally, these glues dampen the paper and this makes the fibers swell perpendicular to the direction of the grain. However, no one wants a tubular book; we can't allow the endsheets, for example, to curl as we are casing books in. Immediately after the glue is applied to the endsheets, the hard cover is placed over the outside of the book and pressed into contact with the glue. Since the grain still wants to swell but is now being held in place by its contact with the binder's board that forms the case, the endsheet paper will wrinkle unless held firmly under pressure while the moisture evaporates and the glue dries.
　　If the grain on the endsheets is correct--i.e. parallel to the binding edge of the book--the swell in the grain may warp the binders board (which has its grain in the same direction) slightly, but as the glue dries with books under pressure the swollen grain shrinks and this tendency relaxes; books emerge from the press flat, with no wrinkles in the endsheets. If the endsheet grain is perpendicular to the binding edge of the book, however, wrinkles tend to form parallel with the grain, since the board will not swell in this direction. This can also be true when tipping endsheets: even though only a thin bead of glue is used, waves may form in cross-grain endsheets when they are tipped on.
　　Grain direction of the text portion of a hard cover book is usually less of an issue, though color plates on coated stock that need to be tipped into a book should be imposed with the grain parallel to the binding.
　　Sometimes the grain direction of the text of a perfect bound book can be an issue. The hot glue used can in some cases cause waves in the paper if the grain is not parallel to the binding edge. Aligning the paper fibers parallel to the binding edge also maximizes adhesion of the hot-melt glue used in perfect binding.
　　Grain Direction, Scoring, and Folding
　　Grain direction is also a critical issue when imposing cover stock for saddle stitched, perfect bound, or smyth sewn soft cover books or presentation folders. The heavier stocks used for covers and folders are virtually always scored to facilitate clean, reliable folding. Again, grain should run parallel to the fold/score for the best result. Covers imposed against the grain may need special letterpress scoring, and even then may not behave well.
　　Coated vs. Uncoated
　　When clay and other mill coatings are added to paper, they change not only the paper's appearance, but its behavior from the pressroom through the bindery. For the binder, coating affects scoring/folding and glue compatibility. Coated stocks are frequently printed with more ink coverage and additional protective coatings like varnish, UV, etc., which can also affect the bookbinder.
　　Clay-coated stock tends to wrinkle much more easily when dampened by the glues used in case binding. For this reason, coated stocks are rarely used as endsheets. Even the text portion of a book run on coated stock can wrinkle when cased-in if proper care is not taken.
　　When a printed cover is required for a hard cover book, film lamination adds the strength needed for the paper to act as the hinges of the case. Paper alone, even with UV or other coatings, will tear quickly at the hinge if not reinforced with plastic film. Stock for a film-laminated case should be an 80 or 100 lb. coated book weight, with a gluable film laminate on the outside only. Several manufacturers now make relatively heavy uncoated stocks suitable both for lithography or foil stamping and use as case material.
　　Coated text stocks can be very difficult to perfect bind; hot melt glue does not adhere reliably to these papers. For best results these books should be smyth sewn before attaching the covers.
　　Coated-1 side (C1S) and coated-2-side (C2S) cover stocks both work well on the perfect binder. It is, however, very important to make sure any and all inks, varnishes, or other coatings are left off the glue area inside.