Chapter 21 Substrates 393
16-lb. stock is thinner than 20-lb. stock. The basic
size of book paper is 25″ × 38″. The substance weight
of book paper is 2 1/2 times the weight of bond with
2 1/2 times the surface area.
Cover paper has a basic size of 20″ × 26″. It is a
durable stock with many textures. It comes in 60-lb.
to 80-lb. weights. The basic size of index stock is
25 1/2″ × 30 1/2″. It is a heavy stock and often
identifi ed by the number of plies. One-ply equals
90-lb. stock; two-ply equals 110-lb. stock; three-ply
equals 140-lb. stock.
Basis weight is the weight in pounds of one ream
of basic-sized stock. A ream has 500 sheets. Usually
paper is referred to by its ream weight, as in 20-lb.
bond or 70-lb. book. A 20-lb. bond means that 500
sheets of 17″ × 22″ writing paper weigh 20 pounds.
If the letter M appears after the weight, it means
per 1000 sheets. For example, 25 × 38 – 140M
means 1000 sheets of 25″ × 38″ book paper weigh
140 pounds, Figure 21-15.
Substance weight is the actual weight of the
ream. Papers have many basic sizes and basis
weights. Therefore, the thickness of a ream of stock
can vary based on its substance weight.
Equivalent weight is the weight of one ream of
paper that is of a size larger or smaller than the basic size.
Use the following formula to fi nd the equivalent weight of
paper, referring to Figure 21-15 for the basic size.
Weights
26
32
40
48
56
64
etc.
100
120
130
160
180
etc.
60
70
80
90
100
120
140
160
etc.
117
144
182
222
286
etc.
Basic Size
17″ × 22″
20″ × 26″
25″ × 38″
25 1/2″ × 30 1/2″
Type
Writing
Cover
Book
Index bristol
Figure 21-15. Some typical weights of paper for common sizes.
grain long: Important factor of paper that can affect folding and direction of feed for printing.
grain short: Indicates that the grain runs across the paper.
paper fl atness: How well a sheet of paper remains straight or unwarped for feeding through a sheet-fed press.
grades: Categories or classes of paper.
basic size: The standard length and width, in inches, of a grade of paper.
ream: Five hundred sheets of paper.
substance weight: The actual weight of a ream of paper.
equivalent weight: The weight of one ream of paper of a size that is larger or smaller than the basic size.