> I looked up the 120 Rasant and it has a cotton coating surrounding the core of polyester.
> Is this right? I thought cotton was a poor choice because of how it would break down.
Ah, now we get technical. Let's look at 3 options:
1) Pure PE: strong, doesn't degrade, but can tangle and be tricky to handle. Can melt when going through a hot needle – after high speed sewing. That is disastrous!
2) Blended cotton/PE: cheap to make, can melt at speed. Many consumer brands.
3) Core-spun PE/cotton: strong PE core with cotton fibres wrapped around the outside. The cotton protects the PE core against the hot needle at high speed. The cotton does not contribute all that much strength, but the PE core provides that anyhow. The cotton can protect the PE core from other hazards like UV.
So professionals often use core-spun PE/cotton for high-speed sewing where strength and quality matters. Rasant is this.
If you want greater strength the right move would be to a bonded nylon. That is what I use for packs. Nylon has a higher melting point, and heavy sewing is usually done at a slower speed. But nylon thread is dearer.
Cheers
