It depends somewhat on brand. I have used YLI nylon monofilament in the bobbin with no problems. There are some things you need to know. This type of thread stretches, so you need to wind the bobbin slowly. If you use plastic bobbins, fill only a little more than half full; if filled full, it likely will distort the bobbin. If you use metal bobbins, you can fill up to 3/4s full. Reduce upper tension in your machine.