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CALENDERING (note the
spelling) is a step in the papermaking process that imparts a smooth
surface to the paper. It's done by running the paper through a stack of
calendering rolls--metal cylinders that compress the fibers and reduce
the bulk of the paper. "Supercalendering" produces an ultra-smooth,
ultra- thin surfaced paper that can be used to print skinny books that
have a lot of pages. The trade-offs are loss of opacity and decreased
durability.
BASIS WEIGHT is the weight
in pounds of a ream (500 sheets) in the basic size for that grade.
Example: Basis 70 means that a 500-sheet stack of 25x38" book paper
weighs 70 pounds. The basic size is not the same for all grades--each
category has a size used to compute its basis weights.
The basic size for text, coated, and uncoated papers--in
other words, for the papers most widely used in publishing--is 25x38".
Understanding basis weight is important because mills and paper
merchants sell paper by the pound, not by the number of sheets or the
length of the web.
CALIPER is the measurement
of a paper's thickness, expressed as a point size in thousands of an
inch. One point equals 1/1000 of an inch. A 7pt. stock is .007" thick.
(A caliper "point" is not the same as a typeface "point," which is 1/72
of an inch--about 14 times as large.) The smaller the caliper, the more
pages per inch (ppi), and vice versa.
Caliper is not related to basis weight. Two papers of
the same basis weight may be of different thicknesses. That is why we
use the term:
BULK to refer to a paper's
thickness relative to its basis weight. For example, an uncoated paper
might be said to "bulk" higher than coated paper.
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