Manufacturer · Fashion & Home Accessories
Bonded nylon thread is a twisted polyamide thread coated with a resin that bonds the plies into one smooth, strong strand. The coating prevents fraying, reduces friction in the needle and allows high-speed sewing through thick leather and several layers of material. That is why bonded polyamide thread is the main machine thread in footwear production, leather goods and upholstery.
Bonded nylon thread: what "bonded" means
An ordinary multi-ply thread consists of several twisted plies. When sewing dense materials, they rub in the eye of the needle and in the leather, begin to separate and the thread breaks. With bonded thread, the finished twisted strand passes through a resin bath and a heating zone. The resin cures and coats the thread with a thin layer, while the plies stay bonded to each other.
The result is a thread that:
- does not fray when cut or when passing through the needle repeatedly;
- has less friction and heats up less at high speed;
- is more resistant to abrasion on the surface of the product;
- forms a stable, even loop, which reduces skipped stitches.
Why polyamide (nylon) for leather and footwear
Polyamide has a very high breaking strength relative to its thickness and good abrasion resistance. It is also slightly elastic – with every step, the shoe upper flexes, and the seam must absorb the movement without tearing the leather or itself. This combination of strength and flexibility makes bonded nylon thread the standard for:
- seams on shoe uppers (closing, joining components);
- bags, backpacks, suitcases and cases;
- machine-stitched belts and straps;
- leather jackets and garments with heavy seams;
- furniture upholstery and seats.
Car interiors are subject to stricter requirements for light fastness and flammability – see our threads for the automotive industry.
Bonded nylon or bonded polyester
| Property | Bonded polyamide | Bonded polyester |
|---|---|---|
| Breaking strength | Very high | High, slightly lower at the same thickness |
| Elasticity | Greater, absorbs flexing | Lower, more stable seam |
| UV resistance | Lower, light colours may yellow | Good, colour is retained |
| Moisture resistance | Good, absorbs a little moisture | Very good |
| Typical use | Footwear, bags, indoor products | Outdoor products, visible decorative stitching |
The practical rule: if the product will spend a long time in the sun – saddles, garden furniture, boats, motorcycle accessories – choose bonded polyester. For footwear, bags and leather goods that are worn and stored mainly indoors, bonded nylon is the classic choice.
Soft and hard bonding
The amount of resin determines how stiff the thread is. With soft bonding, the thread stays flexible and soft and sits more snugly in the seam – it is suitable for shoe uppers and garments. With heavier bonding, the thread is stiffer, smoother and even more resistant to abrasion, which is an advantage for heavy products and automated machines. Many thread manufacturers also add a silicone or wax lubricant on top of the coating to further reduce friction and needle heat.
How thickness is designated
Bonded threads are usually designated in Tex – the mass in grams of 1000 m of thread. In the trade, the American designation with the letter V, which is approximately equal to Tex, is also common. The most widely used thicknesses for leather are:
- Tex 45 (V46) – thin leathers, garments, gloves, inner seams;
- Tex 70 (V69) – the most versatile thickness for footwear, bags and upholstery;
- Tex 90 (V92) – bolder seams, backpacks, heavy bags;
- Tex 135 (V138) – decorative stitching, belts, heavy products;
- Tex 210 and above – saddlery, heavy belts, special machines.
Machine settings for bonded nylon
- Needle. Use a leather needle with a cutting point and a size matched to the thread thickness. The thread must pass freely through the eye.
- Bobbin thread. The bobbin thread is often one size thinner than the needle thread, so that more fits on the bobbin and the stitch is balanced.
- Tension. Bonded thread is smooth, and with tension that is too weak it forms loops underneath. Set the tension on a test strip of the same leather.
- Stitch length. With thick thread the stitch must be longer – dense stitches with thick thread perforate the leather.
How to recognise quality bonded thread
- Even thickness. Run a few metres between your fingers – you should not feel thick and thin sections.
- Complete coating. When cut, the end should not separate into individual plies.
- Stable winding. The cone unwinds evenly, without loops and without the thread twisting on itself.
- Consistent colour within the batch. In series production, order the quantity for the style in one go so that there is no difference in shade.
Storage
Protect spools and cones from direct sunlight, especially light polyamide colours. Old cones that have stood on a windowsill for a long time can lose some of their strength without it showing. For serious orders, always test the thread with a trial seam. You will also find general advice on sewing threads in our sewing threads category.
Bonded nylon threads wholesale from Polkom
Polkom supplies bonded polyamide and polyester threads wholesale in our threads for footwear and leather category – in black, brown, beige, white and fashion colours, with shade matching to your sample. Send us the type of product, the leather and your machines via our contact page and we will suggest a suitable thickness and samples.
