Below are general guidelines for thread/needle compatibility relevant to bag making on an industrial walking-foot machine. This is one of the first questions I see asked in the bag-making groups when makers first order their industrial-walking foot machines such as the 1181 or 1541.
The specific thread fiber (Poly or Nylon) and Tex size will depend on the density and thickness of the fabric you are sewing with, along with personal preference. The specific brand you select may also have a bearing as some industrial thread may be constructed differently (with or without a core) and/or be more/less heavily bonded than another. Industrial thread is typically “Bonded” (“treated/coated”) to withstand the speed and rigor of walking foot machines. This is as compared to a domestic thread which is left “soft” (and not bonded.)
Generally Nylon is stronger than Poly, but Poly is more color fast. However, some sewers prefer the Poly because it feels less “wiry” than Nylon, but this may also depend on the brand. I also prefer bonded thread because it tends to maintain its integrity when when sewing through (gummy) double-sided-tapes.
It is my experience you can use a thinner Nylon (versus Poly) for construction, which I personally prefer because a thinner Tex also allows you to use a smaller needle, which in turn makes smaller holes in your fabric.
However, it also depends on the fabric, particularly vinyl. With some vinyl using a thinner nylon (with too narrow a stitch width), you can actually perforate your fabric which will cause a ripped seam.
Non-Walking Foot Industrial - When constructing linings on my Juki 8700, (especially if using a waterproof canvas) I still tend to use a Bonded thread versus soft thread, but in a thinner Tex, such as T30-T45. But you can also use a Spun-Poly, or soft upholstery thread ("soft" thread), especially if you are using an interfaced woven such as cotton. The fabric fiber (e.g. natural versus synthetic) you are sewing also has a bearing on choice with the 8700.
Which Brand? This is going to be a personal preference. However, the brand I personally recommend is Amann. Amann is more expensive, but it runs through walking-foot machines smoothly and doesn't shred. Amann is more heavily bonded, and in many colors it has a slight reflective sheen which makes the colors very flexible to work across different hues, and shades/tints of a color. I get mine from Sunny Sewing Machines here --
When working with vinyl, I prefer a T70 thread with a #18 needle for most all of my construction. In some construction situations and especially for topstitching, I use a T90 with a #19 needle. When topstitching or sewing through 3+ layers or a dense vinyl (e.g. a strap or topstitching connectors), a #19 needle is a good idea. Depending on the colors I am working with I will switch to a T90 in Bonded Poly for topstitching when I want my topstitching to pop.
When working with a chrome-tanned leather I most often use a #19 sized needle regardless if using a T70 or T90 thread. If the leather is thicker and/or layered, I occasionally use a #20 with a T90 Bonded Nylon. In general with leather I predominantly use Bonded Nylon.
You wil find find these compatibility charts below helpful.