Sewing thread is an essential part of shoe manufacturing and has a large impact on the strength of the seam, durability, shoe’s look, and product quality. Whether used in casual wear or for heavy-duty applications such as boots and sports footwear, the thread has to be able to meet various mechanical stresses and conditions. With an understanding of the sewing thread specifications, footwear manufacturers are able to choose the right sewing threads, reduce production defects and provide quality stitching for each project.
Three important factors in thread selection are strength, size, and performance. Other characteristics that are important to the construction of a shoe are abrasion resistance, elongation, colorfastness, and resistance to heat.
Table of Contents
Understanding Thread Strength
How strong it is when it is being pulled. Foot ware seams have a tendency to be subjected to repetitive movement, friction, bending and tension throughout their everyday wear. So it can be very important to choose a thread that has the right strength and integrity to ensure that seams don’t fail.
When it comes to rugged footwear like boots for the workplace or hiking boots, extra tough threads might be needed to keep these shoes in good condition during tougher times. A certain level of strength and flexibility might be required in lightweight shoes and light upper materials.
One should not simply make the selection of shoe type and then recommend strength of thread; the strength with which the shoe is to be loaded should be kept in mind. But if the thread is too strong, it will fail to overcome weak materials, inadequate stitching or construction of the seams.
Selecting the Correct Thread Size
Thread size affects the size of seams, the type of stitch made with it, and the position of the underside of the thread and fabric through which the needle passes. Thicker threads are typically used for strong seams or intricate designs, whereas thinner threads work well with light fabrics and delicate fabrics.
Thread size may be expressed through systems such as Tex, ticket number, and denier. The systems used are sometimes not conventional, so manufacturers should find out what measurement system is used in the supplier’s technical specification.
When selecting thread size, footwear manufacturers should evaluate:
- Leather thickness: Thicker leather and multi-layer material constructions may need thicker threads.
- Needle compatibility: It is important that the needle can hold the thread without excessive friction or damage.
- Stitch appearance: Thread size should complement the desired seam profile and overall design.
- Seam specifications: Different requirements for structural as opposed to decorative stitching.
The wrong size will damage the needle or create an imprecise knit stitch, bulky stitches, or weak stitches.
Choosing the Right Thread Material
Thread composition is part of its durability, flexibility and ability to withstand environmental factors. The useful mechanical properties make polyester and nylon preferred for use in footwear.
Polyester sewing thread has good strength, colour stability and abrasion resistance properties, making them appropriate for use in various footwear constructions. Nylon sewing thread can be used for high strength and flexibility, especially in parts that undergo repeated actions and wear.
Bonded threads are also utilized in producing footwear. They have a surface treatment that can improve the cohesiveness and handling of the threads when sewing, including in challenging applications.
The decision should be made based on the type of material, types of machines, seam placement and end use characteristics of the shoes.
Evaluating Abrasion Resistance
The continuous rubbing of seams on other surfaces, particularly the sole, heel, toe and side panels of footwear. If it does not have the abrasion resistance then there is a risk of threads wearing out, which makes the product less durable and affects the durability of the seam.
It is the duty of the manufacturer to choose the best threads that are fitting for the friction and wear that were anticipated. A variety of factors affecting the abrasion properties – such as construction, fibre type, surface finish, and seam placement, are affected by a thread.
Under representative wear test conditions, testing can be carried out to identify potential weaknesses before products come to market.
Considering Elongation and Flexibility
Elongation is the extent to which a thread will stretch while under tensional stress until it fails. Elongation determines that a seamless has enough pull without the thread or fabrics getting stressed.
Thread for flexible shoes such as sports shoes, or shoes with flexible upper parts might require a thread that can bend back and forth as they move around. Depending upon the application, however, too much or too little elongation will have an impact on seam stability.
Manufacturers should consider the elasticity of the thread, the flexibility of the material, stitch density and the way the threads are seamed together.
Heat Resistance and Colorfastness
In the manufacture of footwear, threads could come into contact with friction produced by high speed sewing, and/or heat or chemicals in subsequent manufacturing steps. Due to these factors these conditions need to be taken into consideration when selecting a thread to reduce the likelihood of damage and ensure thread performs evenly throughout the usage.
Colorfastness for footwear that has decorative exposed seams is also significant. Textures should not lose color and will not bleed into other colors during laundering, exposure and finishing.
These properties are tested under relevant production and end use conditions to ensure reliable results.
Testing Thread Performance Before Production
It is important to have technical specification objectives as a basic guideline, but practical testing will verify whether a specific thread is appropriate for a specific footwear design. The tensile strength, stitch uniformity, abrasion resistance, seam quality, and finishing conditions should be evaluated.
Other factors, including thread breakage, skipped stitches, tension stability and needle compatibility, should be considered in sewing trials as well. These inspections minimize material use and rework and are useful in the identification of early production issues.
Conclusion
When choosing sewing thread for footwear, it is necessary to comprehensively consider strength, size, material nature, abrasion resistance, flexibility and other properties. The ideal thread will be able to perform the sewing operation in an efficient manner, look good on both the inside and outside of the shoes, and have the structural properties required to do its job.
Manufacturers evaluate technical specifications and perform application-specific trials to enhance the reliability of seams, minimize production defects, and develop shoes that will ultimately deliver comfort and durability for the end user.
