If we're talking piecing (sewing the top together), I use 50 wt. (usually Gutermann or Masterpiece) or 60 wt. Presencia (the Presencia seems thicker than other threads). For quilting the 3 layers together by machine, I use 40 wt. For hand quilting the 3 layers together, I use hand quilting thread, which is thicker and more wiry than regular sewing thread.