'Bobbin' thread is a finer cotton thread used mainly for machine embroidery, to help keep the bulk of thread on the back of the embroidery to a minimum. One can also use the same rayon or polyester thread as on the top in the bobbin.

I think they count on people being math challenged and not being able to figure out how much that "cheap" thread really costs.

Most major brands produce bobbin thread and mark the spool as such. I never buy it. I always use a 30 weight cotton to piece, and anything I like that matches what quilt design I want. I don't pay attention to weight, but I do wind the bobbin with the same thread I'm going to quilt with. I mostly use rayon or polyester, but there are many brands who produce cotton for machine piecing (it's not waxed like most hand quilting thread). Even then I use the same cotton thread in my bobbin as I quilt the top with. I do make sure the bobbin thread will match my backing color. I'm not sure where the "quilt with cotton" thread on cotton fabric got started--I heard it years ago when I first started quilting. Boy would my Holiday pieces look dull if I'd stuck to that rule! Worst of all, I've resorted to using any bobbin at hand that had the color I needed, I've even put the bobbin on the upper spool when necessary. Hope the quilt police don't knock on my door.

"The person" doesn't know what they are talking about. Just repeating misinformation that has been around for years. Use whatever thread you have. It is best if both thread is of similar weight.

The first 3 are listed as 50weight, so what ever 50wt you are using on the top will be fine for the bobbin.

I have always used the same thread in the bobbin that I have on the spool. I keep each bobbin (or bobbins) with its spool in a divided box made of see through plastic. The threads that I buy the most are either Coats and Clark, or Connecting Threads.

I have been using machine embroidery (poly) for my FMQ and love it, I get it from: http://www.metroemb.com/store/, they have fabulous prices and customer service.

I use what ever I am using on the top for my bobbin if I am piecing. I use bobbin thread on the bobbin if I am doing machine embroidery. I also use a thinner thread on my bobbin like bobbin thread if I am doing stippling on some of my crafts, like pot holders, table toppers and small quilts. Hope this answers your question.

I have used the same thread top and bottom in most of my quilts without issue.

The bobbin thread is most likely for use in machine embroidery. It does take a different weight when you are doing embroidery.