Twill Weaves

Twill weaves are the weaves that find a wide range of application. They can be constructed in a variety of ways. The main feature of these weaves that distinguishes from other types is the presence of pronounced diagonal lines that run along the width of the fabric.

The basic characteristics of twill weaves are:

• They form diagonal lines from one selvedge to another.
• More ends per unit area and picks per unit area than plain cloth.
• Less binding points than plain cloth
• Better cover than plain weave
• More cloth thickness and mass per unit area.

Classification of Twill Weaves

The twill weaves are produced in a wide variety of forms. They are however classified broadly into important categories, namely:

• Ordinary or continuous twills
• Zigzag, pointed or wavy twills
• Rearranged twills such as satin/sateen weaves and corkscrew weaves
• Combination twills
• Broken twills
• Figured and other related twill weaves

The above types of twills are further subclassified as:

• Warp face twills
• Weft face twills
• Warp and weft face twills

Continuous Twills

Warp Faced Twills

In these types of twills, the warp thread floats over all the picks in a repeat except one pick. The minimum repeat size required is 3. Examples of warp-faced twills are 2/1, 3/1, 4/1, 5/1 etc.

Weft Faced Twills

These twills are the reverse of the previous ones. In these weaves, the weft thread floats over the warp on all picks in a repeat except one. Examples of weft-faced twills are 1/2, 1/3, 1/4, 1/5 etc.

In figure, B, C, and D show a right-handed or ‘Z’ twill and Fig. A shows left-handed or ‘S’ twill.

Balanced and Unbalanced Twills

In these types of twills, the warp and weft floats may be equal or unequal. In other words, the twills may be of the reversible or irreversible types. Accordingly, they may be known as balanced and unbalanced twills. Examples of balanced twills are 2/2, 3/3, 4/4, 5/5 etc. Examples of unbalanced twills are 2/3, 4/2, 5/3 etc. The 2/2 twill is popularly known as “Gaberdine” weave. Fig. 4.3 A and B show designs for balanced and unbalanced twills and C and D show the interlacement diagrams of a 4/1 twill and 1/4 twill (warp-faced) (weft faced).

Warp and Weft Faced Twills

In these twills, the warp and weft floats may be equal or unequal with either the warp floats predominating the weft floats and vice versa. Some examples of these twills are shown in Fig. 4.4 A, B and C respectively.

Drawing a regular twill on design paper

In a regular twill the ends interlace with the picks in exactly the same way as the picks interlace with the ends, so the whole weave can be described by the order of lifts on its first pick. This order is called the base of the twill. A base written as 2 up, 3 down, 1 up, 2 down means that on the first pick the first two ends are raised, the next three are lowered, the next one is raised and the last two are lowered. The numbers add up to 8, so the twill repeats on 8 ends and 8 picks.

To draw any regular twill from its base:

1. Mark a square of design paper with as many ends and picks as the numbers in the base add up to.
2. On the first (bottom) pick, fill in the squares of the ends to be raised, reading from left to right.
3. On the next pick up, repeat the same marks moved one square to the right for a right-hand twill, or one square to the left for a left-hand twill.
4. A mark that would fall past the last end of the repeat goes on the first end instead, because the first end of the next repeat is the same as the first end of this one.
5. Carry on pick by pick until there are as many picks as ends. The weave is then complete.

Only the raised squares need to be moved; the blank squares follow automatically. Drawing a second repeat beside the first is a quick check that the twill lines run on without a break.

The Angle of Twills

The angle of twill is the angle between the diagonal twill line and an imaginary horizontal line or an axis parallel to the weft. This angle is dependent on the ratio between the ends/inch and picks/inch in the cloth.

When the warp ends/inch is equal to the weft picks/inch, the twill angle will be 45°. When the warp ends/inch exceeds the weft picks/inch the twill angle will be an obtuse angle i.e., >45° (high angle or steep twill). When the weft picks/inch exceeds the warp ends/inch, the twill angle will be an acute angle i.e., <45° (low angle or flat twill).

What makes a twill line prominent

Two cloths woven with the same twill can show the diagonal clearly or hardly at all. Four things decide how prominent the twill line is.

• The yarn. Coarse yarns give a bolder twill than fine yarns, and folded (ply) yarns give a bolder twill than singles.
• The weave. Longer floats show the twill more strongly than short ones, provided the sett is raised to keep the cloth firm.
• The sett. The more ends and picks per inch, the more prominent the twill.
• Twist direction against twill direction. When the yarn twist runs opposite to the twill, the twill stands out: a Z (right-hand) twill woven with S-twist yarn, or an S (left-hand) twill woven with Z-twist yarn. When twist and twill run the same way, Z twill with Z-twist yarn or S twill with S-twist yarn, the twill line is flatter and less distinct.

Firmness and cover: why intersections matter

Every time a thread passes from the face of the cloth to the back it takes up space that could otherwise hold another thread. The figure compares three twills on the same eight-thread repeat. In the 4/4 twill (A) each thread changes sides twice per repeat, so eight threads need the width of about ten thread diameters. In the 3/2 1/2 twill (B) there are four changes, and the eight threads need about twelve diameters. In the 3/1 1/1 1/1 twill (C) there are six changes and they need about fourteen.

So the weave with the fewest intersections (A) can be set closest and gives the most cover, but it is the least firm. The weave with the most intersections (C) is the firmest and gives the least cover, and B lies between them.

End use of Twills

Twill weaves find a wide range of application such as drill cloth, khaki uniforms, denim cloth, blankets, shirtings, hangings and soft furnishings.

Rearranged twills: satin and sateen

A rearranged twill is made by taking the ends (or picks) of a continuous twill in a different order. The best-known rearranged twills are the satin weaves. Satin is the warp-faced form and sateen the weft-faced form, so a satin seen from the back is a sateen. Satins and sateens have these features:

• Each end and each pick interlaces only once in a repeat, so the floats are as long as the repeat allows.
• The interlacing points are scattered so that they do not touch, and no twill line shows. The long floats give the smooth, lustrous surface.
• With so few interlacings, more ends and picks per inch can be fitted in, giving a heavier and closer cloth.
• The threads move easily, so seams slip more readily than in plain or twill cloths, and the long floats snag.

Choosing the move number

A regular satin is drawn by placing one interlacing on each end, and moving up a fixed number of picks from one end to the next. That number is the move number, also called the step or counter. For a regular satin the move number must be more than 1, less than the repeat minus 1, and share no common factor with the repeat. A move number and the repeat minus that number give the same satin, one the mirror image of the other.

Placing a satin and a sateen of the same repeat side by side gives a stripe, and alternating them in both directions gives a check. Because the face of one block is warp and the face of the next is weft, the blocks reflect light differently even in a single colour.