Page 188 - Graphic Design and Print Production Fundamentals

6.5 Paper Basics

Roberto Medeiros

When talking about substrates used in printing, paper is usually what comes to mind. Paper is made most
commonly from wood fibre. Today, many papers also have some percentage of recycled fibre as well
as fillers and other additives. These all contribute to the quality of the paper itself and to the quality of
the printed output. It’s important to understand some basic attributes of paper as they all have a direct
impact on imaging processes and results.

Formation

Formation refers to the distribution of fibres, fillers, and additives in paper and how evenly they come
together. When you hold a sheet up to a strong light source and look through it, the mix of dark and light
areas are the result of formation. The more uniform the formation, the less mottling is observed in the
paper. Papers with uniform formation accept inks and toners more evenly, have reduced print mottling,
and enhance clarity.

Opacity

In strict terms, opacity is the degree to which light is prevented from travelling through a paper. In
practical terms, it’s how well a paper prevents the image on the backside of a sheet showing through to
the front. This is measured on a scale from 1 to 100, where 100 is completely opaque. Opacity can be
increased with fillers, pigments, or even coatings. In general, a thicker paper, coloured paper, or coated
paper is more opaque than its counterparts. Opacity values are very important when projects require
thinner paper stocks and both sides of the sheet are being printed.

Basis Weight and Grammage

When looking at the label on a ream of paper used in North America, you usually see two weight
designations: the basis weight, designated in pounds (#) and the equivalent grammage, in grams per
2
square metre (g/m or gsm). In most of the world, grammage is primarily used. In North America, the
basis weight is more common. Grammage is simply how many grams per square metre paper weighs.
No other factors are represented by this designation. So we can deduce that the higher the grammage, the
thicker or denser the sheet. Basis weight is the weight of 500 sheets of paper at a specific size, known as
the ‘parent’ sheet size, which varies based on the historical use of the specific paper. To understand this
better, let’s examine two different basis weights.

Cover basis weight is based on a 20″ x 26″ parent sheet. So 500 sheets of 80# cover (the # symbol is
used to indicate pounds) at the parent sheet size weighs 80 pounds. Likewise, 500 sheets of 80# text at
the text-weight parent sheet size of 25″ x 38″ also weighs 80 pounds. This can be very confusing as a cut

176