Originally Posted by
Prism99
Metal bobbins hold up better over time and are less likely to distort. However, you should use metal bobbins only in machines that were made for them. A lot of the newer machines come with plastic bobbins; using metal bobbins in them can damage the bobbin case.
I agree, it just doesn't seem that something plastic would work in such an important part of the sewing machine. Bernina doesn't offer them so I have never used them and I wouldn't have even if they offered them.