I have seen several posts about monofilament (invisible) thread. It is usually recommended that you use monofilament thread on the top only, NOT in the bobbin. That said, there are always exceptions to any rule, but normally it is not used top and bobbin. I use cotton, poly, or Bottom Line in my bobbin when sewing with monofilament. BTW, please do not use monofilament thread in quilts for babies or children. If they catch a finger or toe in a monofilament thread loop, it can have dire consequences. Project Linus will not accept baby quilts with monofilament thread.