Metler Silk Finish thread is 100% cotton with a silky, smooth finish. It's my favorite thread for hand and machine work. 100% cotton threads tend to curl. There are two things I've learned to prevent so much curling when hand sewing. 1. If you thread the needle with the thread end that you start pulling from, it doesn't twist as much. 2. If you double the thread, be gentle when you bring the ends together to tie the knot. Don't smash the thread between your fingers all the way down the thread, just catch the ends together and tie the knot.