For the footwear industry, the sewing thread is regarded as a minor expense compared to other materials like leather, mesh, rubber, foam, or synthetic fabrics. The thread serves as an important linkage, though, among the various parts of the shoe and helps to keep it all connected together. The environment can have a significant impact on its performance, especially as it relates to temperature.
Footwear can be subjected to superheating conditions in factories, direct exposure to the sun, heated storage areas, cold climates, freezing temperatures and varying temperatures while in transit and use. These conditions can impact the strength, flexibility, elongation and durability of sewing threads. To understand the effect of temperature extremes on the function of the thread and how these effects relate to the selection of threads and the design of shoe interaction with the body to ensure its reliability in harsh conditions.
The Effect Of Heat On Sewing Threads
Many thread materials have physical characteristics that vary with high temperatures. This effect is a function of the type of fibre, construction of the thread, finish, length of exposure, and temperature of exposure.
If materials used in footwear are heated too severely, some of the synthetic threads may get soft or lose some valuable mechanical properties. Excessive exposure can also cause skin to age faster, especially when it occurs in conjunction with sunlight, water, or chemicals.
Problems with thread caused by the heat include:
- Reduced tensile strength
- Changes in elongation
- Softening or deformation
- The absence of protective finishes
- High abrasion risk. Higher risk of abrasion
- Faster material ageing
The effects are especially relevant in footwear for outdoor, industrial, automotive, safety, or high-performance use applications.
High Temperatures During Manufacturing
There can be thread issues before the shoes get to the consumer related to temperature. Manufacturing operations include heat press, moulding, bonding, drying, finishing, and others where the components are subjected to high temperatures.
When subjected to too much heat in these operations, the properties of a sewing thread may change. A good thread in normal seams could weaken if it is subjected to heat on it many times.
Therefore, when choosing which thread to use, a manufacturer should take into account the entire production process, rather than just the normal sewing process.
The Impact of Extreme Cold
Cold weather can pose another set of problems. As the temperature drops, some materials used for threads lose flexibility, become stiffer or have a reduced rate of elongation.
The shoes for cold weather have to have seams which will stretch at low temperatures to keep the shoes moving. If too much tension is put through the thread and it starts to become stiff, yet the top material is still pliable, the seam movement can further strain it.
This may be relevant for winter boots, outdoor shoes, hiking shoes and protective shoes for cold environments.
Low temperatures may lead to the following:
- Reduced thread flexibility
- Stiffness at seams is also increased
- Lower resistance to repeated flexing
- Greater stress concentration
- Increased risk of thread or seam failure
This effect will vary significantly depending on the polymer being used to form threads and materials surrounding the microthread.
Thermal Expansion and Contraction
Changing the temperature has an impact on the thread, but it also impacts other things. Change in temperatures may cause expansion and contraction of various materials used for footwear.
For instance, a synthetic upper, leather panel, adhesive layer and sewing thread can all have different reactions to temperature changes. The repeated expansion and contraction of these parts may cause tension to build up in the seam.
Repeated thermal cycling can lead to:
- Seam distortion
- Changes in stitch tension
- Material fatigue
- Thread stress
- Reduced seam integrity
This makes thermal stability an important consideration for footwear that experiences significant changes between hot and cold environments.
Heat, Moisture, and Humidity COMBINED
The effect of temperature is never the only factor. In real-life environments, shoes may face various challenges, such as sweating, rain, moisture, humidity, and heat.
Some materials may age more rapidly at high temperature and humidity, and the nature of friction and mechanical response of a thread might be affected. Footwear can also be affected by changes on the upper components around the seam in humid conditions.
Therefore, manufacturers should consider the characteristics of the thread when the environment is not just room temperature.
Selecting the Right Thread for Temperature Resistance
The type of thread should depend on the purpose of the footwear. A useful combination of strength, abrasion resistance, dimensional stability, and durability gives polyester sewing thread and other synthetic threads great utility in a wide variety of footwear. Different finishes, however, and different levels of thread construction result in varying levels of resistance to heat and environmental stress.
The following parameters should be taken into consideration by the manufacturers while choosing the thread:
- Expected operating temperature
- Duration of exposure
- Temperature cycling
- Required tensile strength
- Required elongation
- Abrasion resistance
- Exposure to chemicals and water
- The ability to blend with the top materials
- Sewing-machine performance
The point isn’t just that you select the strongest thread. The thread must have a good balance of properties during the intended service life.
Stitch Construction Also Matters
Stitch construction and thread performance cannot be separated and dealt with in isolation. A good thread is as useless as good tools are on a poorly designed tool; they both don’t work.
So, problems related to the stitch density, too light or too tight thread tension, wrong needle size, or incorrect stitch geometry can cause unwanted stress. These weaknesses are likely to be more noticeable when temperatures are extreme.
It is important, however, that manufacturers carefully consider thread selection and stitch construction within the context of achieving optimal performance, rather than independently. And a correctly designed seam distributes loads and lets the thread perform the way it is meant to.
Testing Thread Performance Under Extreme Conditions
Manufacturers can learn about how a thread will perform in various situations through laboratory testing. Samples can be held under controlled temperatures and tested for tensile strength, elongation, abrasion resistance, and seam performance changes.
Thermal cycling tests can be especially useful, as the footwear might endure multiple changes in temperature on the way to, from, and in service.
By testing, you can determine if a specific kind of thread is appropriate for:
- Cold-weather footwear
- Desert and hot-climate footwear
- Industrial safety shoes
- Outdoor hiking footwear
- Sports and performance footwear
- Protective and specialized footwear
Finished seams, not just thread, can give a more realistic idea, as the effect of the thread on the upper surface material can have a significant impact on performance.
Designing Footwear for Extreme Environments
If there is any consideration for product environmental exposure at all, then it needs to be done at an early stage in product design by the manufacturer. Different thread specifications will be needed for one shoe as compared to another that is made to function in freezing temperatures, as the hot-climate shoe might be made with a heavier thickness of thread.
For instance, an outdoor shoe will need to possess both thermal stability and resistance to abrasion in addition to resistance to moisture and flexibility. Heavy-duty shoes might make use of extra reinforcement over the regions of repeated stress.
Reliability can be greatly enhanced with proper stitches, proper stitch density, proper material, proper seam placement, and proper thread (nylon sewing thread).
Conclusion
Sewing thread behavior in footwear can be affected by a considerable change in temperature. Excessive heat can cause acceleration of aging or change mechanical properties; extreme cold temperatures can cause loss of flexibility and increased stress with repetitive movements. Rapid hot and cold temperature fluctuations may present further difficulties, as some shoes may expand at different rates compared to others.
As a manufacturer, being aware of such influences is crucial to creating footwear that is as comfortable, long-lasting, and structurally safe as possible during its useful life. Using suitable fabric and threads for the temperature, testing seams under realistic conditions, and optimizing the stitch can decrease the chances of eventual failure.
With shoes getting better for more extreme conditions, thread that withstands temperature and judiciously engineered stitches and patterns will become more critical than ever. Environmental stress resistance can be very significant, even if it puts itself on relatively insignificantly.
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