The new standard plastic bobbins are molded in ABS plastic which has been chosen primarily for minimising the noise made by the tension string in the groove. Cutouts in end the end plates decrease the weight plus allow you to observe your yarn on the bobbin when spinning. Because ABS is a slightly softer plastic, we did not want them to wear out quicker so have managed to integrate some high quality and very durable polymer bearings inside the bobbin. They are tricky to see but I promise you they are there! We have also added drive pin holes so the plastic bobbins will now work on the Aura.