Airbags are a safety critical product whose manufacturing demands a high quality sewing thread which can withstand demanding sewing conditions and not compromise seam integrity when sewing at high speeds through multiple layers of densely woven fabrics. While some automotive companies still use single-ply monocord threads for the airbag manufacturing process, a 3-ply twisted bonded thread is a better choice as it provides a more secure stitch. To understand why this is, we must explore the difference between the two types of threads.

A single-ply monocord thread is made out of a single nylon filament tow that is lightly twisted and bonded. Single-ply monocord thread has an oval shaped cross section and is traditionally 15-20% finer than twisted threads. It is also generally used to sew less aggressive materials that require multi-directional stitching.

A 3-ply twisted bonded thread has three plies of nylon filaments that are precision twisted and bonded to create a circular cross section that is consistently uniform throughout its length and allows for precise tension control to aid in a balanced stitch. Technology is used to bond and coat the base filaments of the thread which provides excellent ply adhesion, uniform tack levels, and superior abrasion resistance.

These key elements ensure the thread is protected so it can withstand the rigours of an aggressive sewing process through multiple overlapping fabric layers. Three uniquely bonded plies improve stitch security and ensure protection against needle heat and abrasion through the needle eye.

Most importantly, bonded twisted thread distributes its strength across three separate plies unlike monocord thread whose stitch security depends on a single ply. If that single ply breaks for some reason, the whole stitch may unravel.

Second, 3-ply twisted bonded thread has consistent tension control which creates a more balanced, uniform stitch with exceptional seam integrity.

Third, the unique bonding chemistry of 3-ply twisted bonded threads provides excellent ply adhesion and forms a good loop that can withstand heavy duty multi-layer sewing while providing excellent abrasion resistance.

In a single-ply monocord thread, individual fibres are not buried into the yarn bundle and tend to be more on the surface, therefore causing high amounts of filamentation during high speed sewing. In 3-ply twisted bonded threads, plies are not compromised.

Because of low bond adhesion in a single-ply monocord thread, some common problems associated with it are castling, the effect of alternating stitches being slightly offset which in turn pushes the stitch pattern out of line, and looped stitches, which happen when a stitch is not pulled down tight against the fabric being sewn.

A sewing machine requires thickness consistency along the thread length to create balanced tensions and stitch performance. A single-ply monocord thread tends to be more unbalanced (even before stitching) compared to 3-ply twisted bonded threads.

Finally, in addition to better sewing performance, experiments show that a 3-ply twisted bonded thread has much less variation of strength after sewing in comparison to a single-ply monocord thread. This is critical for seam integrity and stitch security.

Coats manufactures Neophil, a high quality twisted bonded airbag sewing thread in multiple TS 16949-certified factories around the world. These threads are designed to withstand demanding sewing conditions while stitching intricate patterns through multiple overlapping layers of densely woven fabric. Compared to single-ply monocord threads, Coats 3-ply twisted bonded threads have better thickness and tension consistency, are not prone to filamentation, show less strength loss in the seam, form strong and balanced stitches, and perform with the highest level of sewing efficiency that is critical for the integrity and security of the airbag seam.

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