Thru-hiker.com has this poly in 40 tex (weight)
enough to last a diy'er a long long time
Suffice to say, thread is as complicated and anything else if examined closely.
There are many many types,weaves, twists, coatings, etc. in manufacturering thread.
The one at thru-hiker is a multi filament, poly wrapped poly, decot tex 40 with a coating (you can't see or feel it) that improves strength and makes it anti wicking and hydrophobic. Compared to a sewing store Gutterman med weight (40) poly it is about +%30 stronger. It also very rarely breaks in the machine as it is high quality. It will feed through needles as small as 65/70 OK.
Not much reason to use anything else on fabrics lighter than about 2-2.5 oz sq/yd. or most all UL and SUL fabrics.
my 2 cents,
"Hydrophobe 100% Polyester Thread
Description: You'll find that our Hydrophobe100% polyester thread is perfect for the vast majority of your gear projects. And as a Thru-Hiker exclusive, its durable Hydrophobe anti-wicking finish keeps water out of your seams better than any thread on the market.