I use silk thread for most of my fmq. It makes my quilting looks much better (can't see the mistakes that much). I use Bottom Line, Sew Fine, Finishing Touch, Invisifill, or Glide, in the color to match the silk thread in the bobbin. The new thin threads available now are really just as nice for machine quilting as the silk threads. Batting makes a big difference when using silk or thin thread. Wool batting works best for me when using thin thread for machine quilting.