We perform Scoring. Scoring is the process of making a ridge that is indented into the paper that makes the paper fold easier. Scoring is mainly used on cardstock, cardboard or heavy paper, lighter weight papers are generally easier to fold and do not require scoring.
The indention is made by using a blunt metal edge from a wheel that compresses the paper into a hinge like area. The hinge is what makes the heavy paper fold smoothly. Scoring also helps the appearance with the persistent guideline also helping reduce the buckle or cracking of the paper when folding. Scored paper helps to maintain the clear coats and inks during the folding process. With thicker paper comes a thicker score. Un-coated sheets as opposed to coated sheets have more fiber cracking which is why you see so many color projects printed on coated sheets.