I use nylon invisible thread a lot. You need to loosen the upper tension because it stretches. It's easier to use regular thread in the bobbin instead of using nylon in the bobbin too. If you do use nylon invisible thread in the bobbin, it's important to wind it slowly so it doesn't stretch as you wind, use a metal bobbin (plastic ones have a tendency to bulge), and underfill the bobbin (no thread outside the edge of the metal bobbin).