Sewing thread construction explained: types, properties and applications

Sewing thread construction describes how fibres or filaments are processed and combined to form a sewing or embroidery thread. The construction type—together with twist, ply and cord—has a decisive influence on properties such as strength, abrasion resistance, elasticity, surface character, sewability and application suitability.

It is important to understand that the construction types are described based on the structure of a single yarn. However, the finished sewing thread usually consists of two or more single yarns that are twisted together.

 The following wiki subpages provide a more detailed overview of various types of thread construction.

Twist

Yarns and threads are twisted by turning them around their own longitudinal axis, thereby tightly binding the fibres or filaments together. This compact twist increases strength and thus determines sewing performance.

There are two directions of rotation, which can be easily distinguished by the letters S and Z. Depending on the direction of rotation, the course of the centre bar of the respective letter corresponds to the diagonal of rotation of the yarn or thread.
 

Single yarns are usually twisted in the S direction, while twisted yarns are twisted in the Z direction. To stabilise the sewing thread and ensure flawless sewing performance, it is important that the yarn and twisted yarn have opposite directions of twist. The determination of the twist direction ‘Z’ for twisted yarns and ‘S’ for single yarns is due to the sewing process on standard double lockstitch machines, for which Z-twisted yarns are better suited. Due to the position of the needle and hook and the associated pull-off direction of the needle thread from the needle eye on double lockstitch machines, Z-twisted sewing threads undergo additional twisting during the sewing process, which does not have a negative effect on the sewing process. S-twisted threads, on the other hand, exhibit the so-called untwisting effect, which can lead to an unattractive seam appearance and sewing problems.

The number of twists is very important for optimum sewability and high performance. Sewing threads with too few twists have a low twist count, i.e. they are ‘open’. This has a negative effect on sewing performance. During the stitch formation process, e.g. on double lockstitch machines, the hook can ‘hit’ the open twist, causing the thread to break. Sewing threads with too high a twist tend to curl and have too much ‘liveliness’. Knots and loops can form, leading to sewing problems and even thread breakage.

Coarser yarns or threads have fewer twists than fine ones. The number of twists is adjusted to the respective fineness and the requirements of the sewing process. AMANN sewing threads therefore have a precisely coordinated number of twists with tight tolerances, which is regularly checked as part of quality assurance.
 

Ply

The ply is another characteristic of sewing thread construction and indicates how many single yarns a twisted thread consists of. Most sewing threads are 2-ply or 3-ply, i.e. they consist of 2 or 3 single yarns. Single-ply and multiple-ply twisted threads are rare.

The use of different plies is illustrated in the AMANN range by the example of the polyester/polyester core spun thread Saba:

The ply has an influence on the sewing performance and the appearance of thread. For decorative seams, 3-ply threads are preferred in the coarse thickness range, as their thread cross-section has an approximately round shape. 2-ply threads, on the other hand, usually have a higher twist and are therefore suitable for demanding sewing operations, e.g. multidirectional sewing machines. For this reason, and due to their flat character, 2-ply threads are preferred for machine embroidery.

Comparison of sewing thread cross-sections

When specifying the sewing thread thickness, the ply can also be included, in the Nm system by adding a slash to the ply number, and in the Tex system by adding a multiplication sign to the number.

Cord

All standard sewing threads are usually single-twist or direct-twist threads. This means that the thread consists of two, three or, in rare cases, four yarns and was produced ‘directly’ from them. In contrast, multi-level or corded threads are made from several yarns. This requires several production steps: from yarn to thread, from thread to corded thread. These yarns are very rare today and are used exclusively in the coarse ticket range when the desired fineness cannot be achieved with the yarn finenesses available on the market.