I too use Coats & Clark duel duty for piecing and the machine quilting version for my quilting of course. :lol: I notice though when I checked the %'s on both there wasn't much difference between the duel duty and the machine quilting as for how much is cotton & how much is polyester. :wink: I'm not sure if the difference is in how it wears/works in the machine when quilting. Perhaps the duel duty would break more with stress on quilting, I haven't tried it to see if that is the case. :?