In the process of being a beginner I got my M. in law's classic little Singer in working order but had to take it to the shop because of a thread breakage problem. I described it to the mechanic, he nodded, said he knew exactly what it was, grabbed a screwdriver, described a minor misalignment problem in a place where I hadn't been, gave it a tweak, put the screws back in, and away she went. He didn't charge me a thing. But, after fixing he he pulled out some of the top thread, pulled it between his hands...snap...he scowled at me. Then he tried the bobbin thread, same result, same scowl. "Good thread doesn't break like that", he said "its hard to break because it digs into your hand so hard."
I figured it broke because it was ages old, but I had just been to Wal-Mart and picked up some shiny new Coats&Clark polyester coated polyester so I was bound to be good. I went home and gave my new thread the test: ...snap...easy as pie. It snapped almost as easy as the old cotton thread in the sewing box. Now I began to visualize sitting on the edge hem of my hammock and hearing popping sounds.
Ok, not to worry, there is a "something Creations Sewing Shoppe" I've seen in town. So I go there and guess what, ...they don't carry polyester thread!! There is hardly a square foot of the walls that is not plastered with a quilt, quilting is all the rage, and they only carry cotton threads. The lady wants to know what in the world I am sewing. I tell her, she is greatly astonished, "hammock, your're making a hammock?", "nylon...you mean like ripstop?", "straps...you're sewing straps"? She thinks for a minute...a light comes on..."Upholstery thread, that's polyester, we have upholstery thread, its good and strong." Oh, hallelujah, saved at last!
I go home with a couple of rolls and sure enough its thick and hell for stout. Threading it through a #11 needle it a real trial but I get her done. The little old granny of a machine i have is very high quality and actually handles the stuff pretty well after some tension adjustment. During the next hour or so of making practice hems out of extra fabric I learn a couple of things about upholstery thread. Number one: there is such a thing as too thick. The difference between the thickness of the thread and the thickness of the nylon fabric is such that a couple of rows of stitches of the big stuff feels like you just installed a miniature zipper on the hem. And, number two: there is such a thing as too strong. During the process of learning to use the machine and tinkering with adjustments I made several bird nests of thread tangles and broke the thread a couple of times...then WHAM...a really nasty one. When I managed to finally hack my way out I found that that the thread didn't break..it ripped the nylon fabric. Like I said, the thread is hell for stout.
I love learning new things and have now formed some opinions re: the use of upholstery thread. IMO it is big time overkill for hammock nylon. You can use it if you don't mind bumpy hems and you don't screw up and rip something. It would probably be good for strapping if you use at least a #14 needle. You will be much better off getting some good quality but ordinary thickness poly thread to make hammocks and gear. Forget the upholstery thread. I just ordered some good stuff on line since there is no place in town to get it.