I have heard of a few people using some type of 'invisible'thread. One lady on my Gammill group says it it not made for long arms. The thread gets too hot and it 'burns' a groove in the tension disks. I would ask where you rent. My favorite 'go to' thread is Permacore. Its sturdy, comes in lots of colors and is not pricey. I also like So Fine for the bobbin..and sometimes for top thread if I need some thing finer. Congrats and have fun!