Manufacturer · Fashion & Home Accessories
Bonded nylon thread is a twisted polyamide thread coated with resin that bonds the fibres into a smooth, strong filament. This coating prevents fraying, reduces needle friction, and enables high-speed sewing through thick leather and multiple layers. That is why bonded nylon thread is the main industrial sewing thread in shoe production, leather goods, and upholstery.
What does “bonded” mean in bonded nylon thread?
Regular multi-ply thread consists of several twisted fibres. When sewing dense materials, these fibres rub against the needle eye and leather, start to separate, and the thread breaks. With bonded thread, the twisted yarn passes through a resin bath and a heating zone. The resin hardens and coats the thread with a thin layer, bonding the fibres together.
The result is a thread that:
- does not fray when cut or after repeated needle passes;
- has less friction and heats less at high sewing speeds;
- is more resistant to abrasion on the product surface;
- forms a stable and even stitch loop, reducing skipped stitches.
Why polyamide (nylon) for leather and shoes?
Polyamide offers very high tensile strength relative to its thickness and good abrasion resistance. It is also slightly elastic – with every step, the upper shoe bends, and the seam must accommodate movement without damaging the leather or thread. This combination of strength and flexibility makes bonded nylon thread the standard for:
- upper shoe seams (preparations, attaching parts);
- bags, backpacks, suitcases, and cases;
- machine-stitched belts and straps;
- leather jackets and garments with heavy seams;
- furniture upholstery and seats.
Automotive interiors require stricter lightfastness and flame retardancy – see threads for the automotive industry.
Bonded nylon vs bonded polyester
| Property | Bonded Polyamide | Bonded Polyester |
|---|---|---|
| Tensile strength | Very high | High, slightly lower at the same thickness |
| Elasticity | Greater, absorbs bending | Lower, more stable seam |
| UV resistance | Lower, light colours may yellow | Good, colour retention |
| Moisture resistance | Good, slightly absorbs moisture | Very good |
| Typical use | Shoes, bags, indoor products | Outdoor products, decorative visible seams |
Practical rule: for products exposed to prolonged sunlight – saddles, garden furniture, boats, motorcycle accessories – choose bonded polyester. For shoes, bags, and leather goods mainly used and stored indoors, bonded nylon is the classic choice.
Soft and hard bonding
The amount of resin determines the thread’s hardness. Soft bonding keeps the thread flexible and soft, allowing it to lie closely in the seam – suitable for shoe uppers and garments. Harder bonding produces a stiffer, smoother, and even more abrasion-resistant thread, ideal for heavy products and automated machines. Many thread manufacturers add silicone or wax lubricant on the coating to further reduce needle friction and heat.
Thread thickness designation
Bonded threads are usually measured in Tex – grams per 1000 metres of thread. The American V-size designation is also common and roughly equals Tex. The most used thicknesses for leather are:
- Tex 45 (V46) – thin leather, garments, gloves, inner seams;
- Tex 70 (V69) – the most universal thickness for shoes, bags, and upholstery;
- Tex 90 (V92) – more visible seams, backpacks, heavy bags;
- Tex 135 (V138) – decorative seams, belts, heavy products;
- Tex 210 and above – saddlery, heavy belts, special machines.
Machine settings for bonded nylon thread
- Needle. Use a leather needle with a cutting point and size matching the thread thickness. The thread must pass freely through the needle eye.
- Bobbin thread. Often the bobbin thread is one size thinner than the top thread to fit more on the bobbin and balance the stitch loop.
- Tension. Bonded thread is smooth and forms loops underneath if tension is too loose. Adjust tension on a test strip of the same leather.
- Stitch length. For thick thread, the stitch length should be longer – dense stitches with thick thread perforate the leather.
How to recognise quality bonded thread
- Even thickness. Run several metres between your fingers – no thick or thin spots should be felt.
- Complete coating. When cut, the end should not separate into individual fibres.
- Stable winding. The cone unwinds evenly, without loops or twisting.
- Consistent colour batch. For serial production, order the full quantity at once to avoid shade differences.
Storage
Keep cones and spools away from direct sunlight, especially light-coloured polyamide. Old cones stored long near windows may lose some strength without visible signs. For large orders, always test the thread on a sample seam. General sewing thread advice is available in the sewing threads category.
Wholesale bonded nylon threads from Polkom
Polkom manufactures wholesale bonded polyamide and polyester threads in the threads for shoes and leather category – available in black, brown, beige, white, and fashion colours, with shade matching on request. Send us details about your product, leather, and machines via the contact page, and we will recommend the suitable thickness and samples.
