I have started useing pre-wound bobbins because my machins is stubborn about winding bobbins and the prewound ones hold so much more thread. I was using one one day at a class they the others gave me a hard time about it saying the thread in them is inferior but I havn't had a problem with them. The first ones I bought seemed to be nylon or polester so I order cotton ones from Connecting Threads and really love them. They save tons of time and aggrivation. That my favorite new find..