Thread types – Nylon vs. Poly

Straight polyester thread is pretty cheap. It is strong enough, but it can be hard to handle as some forms tend to kink in the machine.
Poly-cotton thread is more common and is suitable for a lot of sewing, including clothing. It runs very well.
Bonded nylon thread is dearer but much stronger. It's usually a bit heavier too. Use it for packs.

Cheers

I use nylon occasionally for hand sewing, like repairing boots or something

Common Gutterman Polyester for everything else

The Gutterman is fairly strong, but not strong enough for a pack unless you do several rows. I do a zigzag with 1 mm spacing so the spacing on each side is 2 mm. Then do another zigzag half overlapping, and a couple rows of straight with 2 mm spacing to lock the thread. Goal is to not put two holes in the fabric closer than 2 mm.

If you were sewing quantities of gear for sale, and labor is a major cost, you wouldn't want to do extra rows of stitching, too expensive. Use thicker thread and a commercial sewing machine to save labor costs. I don't think this is applicable to MYOG.

When a row of stitches goes into the corner of a nylon tarp, the nylon fabric stretches but the thread does not, so it breaks. So I put a zigzag stitch for the one foot closest to the corner. The fabric stretches and the seam will stretch without breaking the thread even though the thread does not stretch.