Pitney Bowes DocuMatch Integrated Mail System Reference Manual page 62

Left on the wire cloth is a thin sheet of fibers that, when dried
and given a finish, becomes paper. The fibers in the sheet are
crisscrossed in all directions. Because of the motion of the
conveyer, however, most of the fibers align themselves along
the direction of the sheet motion. This alignment of fibers
gives paper its grain.
There are two sides to a sheet of paper – the wire side and the
felt side (Figure A-2). The wire side is the side next to the wire
cloth. Generally more fibers are found on the wire side of a
sheet of paper. Because the fibers tend to hang through the
mesh, the wire side tends to have a rougher finish than the felt
side. The felt side, as you might expect, is the side next to the
felt rollers. It is the smoother side of a sheet of paper and is
the side printed on (and the first side printed on when in
duplex mode). You can determine which is the felt side and
which is the wire side by examining both sides of a sheet of
letterhead paper closely.
Figure A-2
The two sides of a sheet of paper
DocuMatch ™ Mail Materials Reference Guide
Introduction to Paper • A
F400_024
A-3