Superior Threads sells 100% cotton ones and I've been using them almost exclusively for years and have many colors. I really, really like them! They are too wide for the Feather Weight or the 301, though.

Even on a regular Bernina??? My maintenance woman strongly suggested using only Bernina bobbins when she did the cleaning and found a plastic bobbin in the case. I stopped using them because she said something that made me feel like an idiot. I had never experienced any problems using them in either the Bernina or my older Kenmore.

Are these prewound bobbins made of plastic or paper?

How do you know what machine they will work in.

I have Baby locks and my friend has a Bernina and my plastic bobbins work in her machine.

One of my baby lock machines has a different type of plastic bobbin and will not inter change with my other two baby locks.

ThreadArt has the poly pre-wound bobbins on sale right now - 144 for $30 (The page says that there are 108 to the box, but there are actually 144 in the boxes that I've bought.)
http://www.threadart.com/shop/item.aspx?itemid=4055

This is the plastic-sided Type A bobbin for class 15 bobbin machines and it looks like they're selling for $25-40 per 80 bobbins elsewhere, so there's quite a difference in price. I love the thread in these bobbins, although I would like to find a matte poly or cotton, too.

They carry L and M sizes and in plastic, cardboard and sideless styles, but those aren't one sale at the moment. Still their prices are worth checking.

I got the ones with plastic bobbins but you do need to know what kind of bobbin your machine uses. Mine uses a class A which is a little taller than the usual bobbins

It doesn't appear that anyone answered my question about the cost factor. All appears to say they are convenient but what is the cost compared to winding yourself.

Why not? I have thought about it. I use 7 bobbins when I make a biscuit baby quilt.

I tear the paper off the pre wounds. If the bobbin is wound tight and at the right tension you don't need it in bobbin at all. Self winding will never get you the tightness or perfect tension so you need a bobbin. Paper bobbins usually fit most machines once the paper is torn off.

I think that the conveneince is the key word. You end up with more bobbins, and that would be a plus for me, the bobins are not cheap either. I have not really checked out the prices of prewound bobbins but have seen them. I guess the hard part would be to find them for your mechine.

they are paper bobins?