When paper is made, the fibers that comprise the paper lie in a common direction. The direction of the fibers follows the direction the paper as it travels through a paper machine. These fibers create a grain in the paper. A sheet of paper with the grain direction in the long direction is considered “grain long”. A sheet of paper with the grain direction in the short direction is considered “grain short”. How does this impact you? When you print on paper and when you fold paper, grain is an important, and often critical consideration.
The biggest impact grain direction can have involves cracking. Folding against the grain can cause cracking. This cracking can be particularly pronounced when there is heavy, dark ink coverage over the fold. Generally speaking the thicker the stock the more critical the grain direction becomes when the paper is folded. Sometimes you can fold against the grain if you score the sheet. But more often than not, the best solution is to make sure you fold with the grain.
It is important to work with your printer to address grain direction when you specify a job. If you have a job that folds, has heavy coverage and is on a cover weight stock, ask your printer about cracking on the fold. But beware: even text weight stocks can crack! For standard sized products (generally 8 ½”x11” or 11”x17”) cover weight paper with multiple grain directions is often available to address standard folds. However, if your product is an odd size, the size may dictate the grain direction of the press sheet in order to maximize paper efficiency. However, if this grain direction is perpendicular to the fold direction, your final product may crack when folded.
Another type of job to watch out for involves right angle folds. If your job has folds that are opposite- perpendicular- to one another (commonly known as a right angle fold) one of your folds will be against the grain.
Design is critical when considering grain. To minimize cracking you may want to design your job to avoid printing over the folds. If there is no ink on the folds, cracking can be less pronounced when it is folded.
Of course scoring paper prior to folding can help to minimize cracking, but it is not a guarantee of success. Sometimes, even if grain is in the correct direction and the sheet is scored, you may have cracking. This is often because certain papers are prone to cracking. For example, 80# cover of one brand may crack less than 80# cover of another brand. A common cause for this discrepancy between brands is the moisture content of the sheet. A higher moisture content may reduce cracking. As with most things in life, experience is the best teacher.
It is difficult to avoid cracking but paying attention to grain direction and design can help to minimize problems. The lesson here: involve your printer early on in the process and get their experienced input.