I've used metallic thread and for sure use a metallic needle. Don't use it in the bobbin tho. Just choose a similar colored cotton or poly thread for the bobbin. Sometime the thread spool will have on the label or inside the cone, what size needle to use and what to set your upper tension at. Make sure to practice on a quilt sandwich first to make sure you have everything set correctly, before you try it on your project. As far as invisible thread, I was told about using Superior brand, from a friend. I used it recently and found it to be much better than the last brand I'd used.