As the footwear sector is paying attention to the development of responsible products and to the reduction of dependence on traditional resources, recycled and bio-based materials are becoming more and more common. These alternatives may provide footwear with physical and sewing properties that are different from those of traditional footwear materials, such as recycled polyester uppers (polyester sewing thread), plant-based coatings and bio-based synthetic materials.
Therefore, it is of utmost importance to use the correct sewing thread. Thread should be compatible with the shoe construction, the material and production process, and shoe function.
Understand the Material First
The first step in choosing threads is to first get familiarized with the material being sewn and what it is recycled or bio-based. They can have different thicknesses, flexibilities, surface characteristics, resistance to abrasion and strength against tearing.
Recycled fabrics can vary in their fibre qualities according to the source and process used to manufacture the fabric. Natural fibre textiles as well as new polymer-based materials are potential options for bio-based materials. These qualities are useful for manufacturers to consider when choosing the right thread for their needs.
Match Thread Strength to the Construction
Footwear seams can experience considerable stress during manufacturing and everyday use. This thread should then be strong enough and seam up to the job for that particular type of construction.
Manufacturers should take into account when choosing thread:
- Required seam strength
- Material thickness and construction
- Expected stress on the seam
- Thread size and construction
- Stitch density and stitch type
Not all the time, maximum thread is the goal. There should always be a synergy between the seam and the fabric, because in this way the fabric isn’t unnecessarily damaged by the thread.
Consider Flexibility and Elongation
In many cases, recycled and bio materials used for shoes are intended to be flexible and comfortable. These actions should be matched by the sewing thread.
A thread having an appropriate elongation can withstand repeated movement and ensure the maintainable stitch integrity when flexibility is applied to the seam. This can cause stress raisers in the thread or cause problems in performance or appearance of soft parts.
Especially important for shoes which bend often while walking, running or making use of the foot.
Evaluate Abrasion Resistance
The process and use of shoes can create intra-repetitive friction at the footwear seams. Abrasion should therefore be resisted if it is to be expected particularly when processing materials in areas of constant movement or external contact.
Significant properties to consider are:
- Abrasion resistance
- Seam durability
- Resistance to repeated flexing
- Resistance to environmental exposure
Using abrasion resistant thread may help keep the appearance and performance of the seams for the product’s service life.
Check Compatibility With Sewing Equipment
Materials that are recycled or made from biological products have different sewing performance. They have surface properties, thickness, extensibility and resistance to friction properties, which may affect the penetration of needles and motion of thread.
The type of thread should thus be considered in conjunction with the sewing machine, thread needle, type of stitch, tension of the thread and sewing speed. Setting up the machine correctly can minimize problems like torn thread, those that skip stitches, puckered stitches, and uneven stitches.
Consider Thread Composition
In addition, in situations where sustainability is a significant objective of the product, manufacturers can also assess the sustainable makeup of the sewing thread. Footswear products constructed using recycled materials may be enhanced with recycled-content threads and/or bio-based thread options if suitable to the product needs.
Its problem is, however, that sustainability must be measured on a technical performance criterion, too. However, if there is content recovered or ‘bioresin’ but no corresponding durability and sewing, then the use of a thread with recycled or bio-based content can not be justified.
Evaluate Colour and Appearance
In the field of footwear design, thread is a crucial part of many designs. They should retain even color and texture and even stitching throughout the process.
When choosing to have visible stitching, manufacturers should consider:
- Colour consistency
- Colourfastness
- Surface appearance
- Stitch definition
- Resistance to finishing processes
These are critical when a design is to be embellished with decorative stitching using polyester embroidery thread, or details such as branding.
Test Before Full-Scale Production
A thread has to be tested in a lab and in the production line before being approved for mass production. The assessment needs to assess stitch formation, seam strength, flex, abrasion resistance, thread breakage and appearance.
The thread should also be evaluated to see if it still conforms to specification after any applicable finishing and testing required to determine its performance.
Think: The Complete Picture Of Sustainability
The chosen thread for sustainable footwear isn’t only to consider the raw material. The use of recycled or bio-based content, the production process, durability, expected product life, and compatibility with the product design may be considerations for manufacturers.
The ability to reduce footwear travel seam wear and increase the footwear life can also be a sustainable contribution from the durable thread.
Conclusion
There are several factors to consider when selecting threads for plastics-reuse and bio-based footwear materials, including performance, compatibility, optical properties and sustainability goals. Several factors should be taken into consideration when selecting a type of thread, which are strength, flexibility, abrasion resistance, machine compatibility, and material characteristics.
In this way, manufacturers can guarantee durable seams and contribute to the general push towards more sustainable footwear production by testing the thread and material for the footwear together under realistic production and use conditions.