The brand of thread can make an enormous difference. The only type I have sewed with on my Bernina is YLI brand, which I think is .003mm thick (about same thickness as a strand of fine hair). This type of thread has more stretch than regular thread, so it is necessary to loosen the top tension. When winding a bobbin, use only a metal bobbin (plastic bobbins) can distort, wind slowly to prevent stretching, and underfill the bobbin. With all of this, I can use YLI invisible thread in both top and bobbin without problems.