Manufacturer · Fashion & Home Accessories
An airbag seam in a car seat is a specially designed seam that must tear in a fraction of a second to let the inflating cushion through. That is why the thread, thickness, stitch length and seam type are specified by the vehicle manufacturer. In a repair, the upholsterer must reproduce this specification exactly – a stronger thread is not better, and it can prevent the airbag from deploying.
Airbag seam in the seat: how it works
In many cars, side airbags are built into the backrest of the front seats, usually on the door side. In a collision, the gas generator inflates the cushion and it must exit through the seat cover. Instead of an opening, the cover has a seam designed to tear under the pressure of the cushion. This seam is often marked with an "AIRBAG" label sewn into the seam or close to it.
There is another, more hidden detail: behind the leather in the backrest there may be textile straps or a "sleeve" that guides the cushion precisely towards the seam. These straps are also part of the system and must not be removed or sewn differently during a repair.
Why thread for airbag seams is a safety issue
An airbag seam must be strong enough to withstand getting in and out every day for years and at the same time open predictably when the cushion inflates. This balance is achieved with a strictly defined combination of:
- type and material of the thread;
- thread thickness (tex);
- stitch length and number of stitches per centimetre;
- type of seam and position of the seam allowances;
- material of the cover and the backing.
If the upholsterer replaces the thread with a thicker one, shortens the stitch or adds a second decorative seam across the tear line, the seam becomes stronger than intended. In the worst case, the cushion is delayed, deflected or does not exit correctly. If the thread is too weak, on the other hand, the seam can split in normal use.
Rules for the upholsterer with airbag seats
- Identify the seat. Check for an "AIRBAG" label on the backrest and for cables to the seat. If you are not sure, assume there is an airbag.
- Work according to the manufacturer's instructions. The service documentation for the model describes removing the cover, the position of the seam and its requirements.
- Removing the module is for a qualified specialist. Handling the pyrotechnic element and the electrical part of the airbag is not an upholstery task.
- Do not alter the tear seam. No additional decorative seams, no adhesive and no reinforcing tapes along this line.
- Use the specified thread. If the specification is not available, the safest solution is an original cover or a cover certified as airbag-compatible.
- Sew the "AIRBAG" label back on if it has been removed.
- Document the work – material, thread, stitch – so that there is traceability in any later inspection.
Seat covers and airbags
Off-the-shelf seat covers that are pulled over the original upholstery can also block the side airbag. That is why, on seats with built-in airbags, only covers that the manufacturer explicitly states as compatible are used, usually with a special seam or opening on the airbag side. If you make custom covers, keep in mind that the customer will fit them on a seat with an airbag – this is a responsibility that requires design and testing, not just a good thread.
Which thread is used in the rest of the seat
For all other seams on the seat, the usual rules for automotive upholstery apply: bonded polyamide or polyester thread of medium thickness for construction seams and a heavier polyester thread for visible decorative seams. You will find these threads in the threads for the automotive industry group. It is important not to automatically carry the same thread and stitch over to the airbag seam line if the specification requires something different.
| Seam | Who specifies the thread | Freedom for the upholsterer |
|---|---|---|
| Airbag tear seam | the vehicle manufacturer | none – an exact copy of the specification |
| Construction seams of the backrest | specification or the upholsterer | within good practice |
| Decorative seams | the interior design | as desired, outside the airbag line |
The airbag cushions themselves
The cushions are sewn in specialised production facilities from high-tenacity polyamide fabric and thread, using strict processes and testing. They are not repaired in an upholstery workshop. If the cushion has deployed or is damaged, the whole module is replaced by an authorised service centre.
Retrimming and interior tuning
The greatest risk comes with a complete retrim – new leather, contrast stitching, quilting. The designer wants all panels to look the same, but the airbag line requires a different seam. The solution is for the tear line to remain to the original specification, and for the decorative effect to be achieved in the adjacent panels. Discuss this with the customer in advance and explain why one seam looks different.
The most common mistakes
- Replacing the cover without checking for an "AIRBAG" label.
- Adding a decorative double seam across the tear line.
- Using the strongest thread available "just in case".
- Gluing the leather to the foam in the area where the cushion exits.
- Removing the guide straps behind the cover.
For the construction seams of seats, also see the general range of threads and sewing threads.
Technical threads from Polkom
Polkom is a Bulgarian manufacturer of accessories for fashion, furniture, footwear and bags with over 30 years of experience. We supply technical threads for automotive upholstery and can select a thread to a given specification – type, material, thickness and colour – and send a sample for checking. Send us an inquiry with the specification via Contact.
