Manufacturer · Fashion & Home Accessories
Car seats are sewn with technical synthetic threads – most often bonded polyamide or polyester with a thickness of about tex 70–90 for structural seams and tex 135–210 for visible decorative stitching. The right thread is chosen according to the position of the seam, the seat material (leather, faux leather, Alcantara, textile) and how much sun the interior will be exposed to.
Why car seat threads are a separate category
The seat is the most heavily loaded textile element in a car. Every time someone gets in and out, the seams along the side bolsters bend and rub, and when seated, the tension across the centre panels changes constantly. Add to that temperatures above 60 °C in a parked car in summer, cold in winter, sweat, cleaning products and UV rays through the windows. Ordinary sewing thread for clothing is not designed for this combined load, and after one or two seasons it starts to wear, fade or break.
That is why upholstery workshops work with threads for the automotive industry – continuous synthetic filaments with high tensile strength and a coating that protects them when sewing through dense materials.
How to choose car seat thread: 5 questions
- Is the seam structural or decorative? Structural seams join the panels and are not visible or barely visible. Decorative seams (topstitching) are visible on the surface and define the look of the interior.
- What material is the cover made of? Genuine leather, vinyl (faux leather), Alcantara and dense textiles react differently to the needle and to the thread thickness.
- How much light will the seam receive? The rear seats of a hatchback, convertibles and seats under a large glass roof get much more UV than the front seats of a saloon.
- What machine and needle will be used? Thick decorative thread requires a needle with a larger eye and a machine with suitable feed (most often a walking-foot machine with top and bottom feed).
- Must the colour match the original? When repairing one seat, the colour and thickness of the stitching must match the others.
Thread material: polyamide or polyester
Bonded polyamide (bonded nylon)
Polyamide has very high strength and good elasticity, so it tolerates the flexing of the side bolsters and the stretching of the leather without breaking. The bonding glues the filaments together, reduces friction in the needle and protects the thread from fraying at high sewing speeds. This is the classic choice for internal structural seams.
Polyester
Polyester is slightly less elastic but significantly more resistant to UV rays and keeps its colour longer. That is why it is preferred for visible seams exposed to direct light – the top of the backrest, the headrests and seats in convertibles.
Thread thickness by seam
| Seam type | Indicative thickness | Note |
|---|---|---|
| Panel joining seams | tex 70–90 | strong but unobtrusive seam |
| Piping seams | tex 70–90 | high tension when flexed |
| Single decorative stitch | tex 135 | clearly visible but not coarse |
| Double or French decorative stitch | tex 135–210 | pronounced sporty effect |
The values are a guide. The final choice is made after a test seam on the actual material.
Seat material and thread choice
- Genuine leather – medium to heavy thread and a needle with a cutting point for leather. Stitches that are too dense perforate the leather and weaken it like a postage stamp.
- Vinyl and faux leather – the material does not recover after being pierced, so the stitch length must be greater and the thread smooth so it does not enlarge the holes.
- Alcantara and microfibre – finer decorative seams, often with a thinner thread so the stitching does not "sink" into the soft pile.
- Upholstery textile – structural thread tex 70–90 and a round-point needle that parts the threads without cutting them.
Colour: match or contrast
In factory production, the thread colour is part of the interior specification. For repairs and retrimming there are two approaches: tone-on-tone, when you want the stitching to disappear, and a contrasting colour (red, orange, yellow, blue) when the seat should look sporty. In both cases, check the thread colour in daylight right next to the material – under workshop lamps, black, graphite and navy are easily confused.
If an order for seats will be sewn in several stages, order the thread all at once. This avoids shade differences between batches.
Common mistakes when choosing
- Using cotton or spun polyester clothing thread in loaded seams.
- Too thick a thread with too small a needle – the thread wears in the needle eye and breaks.
- Polyamide for visible seams in a convertible – after a few seasons in the sun it fades and loses strength.
- A very short stitch on leather, which creates a perforation and leads to the material tearing rather than the thread.
- No test seam before the series.
If you also work with leather goods outside the car, see our threads for footwear and leather, as well as the general range of threads.
Car seat threads from Polkom
Polkom is a Bulgarian manufacturer and wholesaler of sewing accessories with over 30 years of experience. For upholstery workshops and automotive interior manufacturers, we supply technical seat threads in various thicknesses and colours, match shades to a reference and send samples for testing. Minimum quantities depend on the article. Send us the material, the seam type and the desired colour via our inquiry form and you will receive a quote.
