Woven Fabrics - Fairchild Books

Uses of Spun and Filament Yarns
Some fabrics are made only of spun yarns, some of only
filament yarns, and others of a combination of spun and
filament yarns. Each type of yarn is best for certain uses.
Spun yarns may provide warmth, softness, and lightness
of weight and are, for example, ideal in fabrics for
T-shirts, sweaters, and blankets. Filament yarns are better
for items where smoothness and luster are desired
because the yarns are finer, more uniform in diameter,
and lustrous. Filament yarn fabrics can offer a smooth,
uniform surface. They are used in linings because their
smoothness makes it easier to slide into and out of
garments. They are also used for the outer shell of ski
jackets, in a tightly packed construction, to resist the
penetration of wind.
Yarn Twist
Yarns are made by twisting together parallel or nearly
parallel fibers. The amount of twist in a yarn is designated
as the turns-per-inch (2.54 centimeters), or TPI,
of the yarns. The TPI in a yarn has an important bearing
on the appearance and durability of the yarn and
the fabric that will be made from it.
Spun yarns with relatively low twist (from 2 to 12
TPI) are frequently called soft-twist yarns because the
yarn is softer, fluffier, and more flexible. They are not as
strong as spun yarns with high twist. Knitting yarns are
usually soft twist.
Spun yarns with relatively high TPI (20 to 30 TPI)
are called hard-twist yarns. The higher twist causes
them to be smoother, firmer, and kinkier than spun
yarns with low twist. They are also stronger.
Filament yarns usually have very low twist (½ to 1
TPI). Twist in filament yarns does not increase strength
but merely serves to keep the filaments in the yarn
together. Some filament yarns are purposely made with
high twist to produce a pebbly, harsh surface effect.
These yarns are called crepe-filament yarns and the
twist is referred to as crepe twist. (See Figure 4.4.)
Twist Direction
In addition to the amount of twist in a yarn, the direction
of the twist is also designated. As shown in Figure 4.5,
there are two types of yarn twist: S and Z. In an S-twist
yarn, the spirals run upward to the left, corresponding
to the direction of the diagonal part of the letter S. In a
Z-twist yarn, the spirals run upward to the right, similar
to the diagonal part of the letter Z. Yarn-twist direction
is not an element of quality because it does not affect
YARNS AND SEWING THREADS
A 71 F
Figure 4.4
A crepe yarn kinks when slackened because of the high twist.
Figure 4.5
S- and Z-twist yarns.
properties such as strength and abrasion resistance.
S- and Z-twist are important to the fabric designer and
stylist because the direction of the twist affects the surface
appearance of fabrics. Crepe fabrics are sometimes
made by combining S- and Z-twist yarns to produce the
balanced, pebbly effect on the fabric surface.
Yarns for the towel business typically are made of
cotton, twisted in a Z direction with a high TPI. This
results in a final product that is relatively hard. Twistless