I think the bobbin thread is alot more fine.

good question the teddy bears i done in projects was fsl and i used regular sewing thread at the bobbin and embroidery thread on the top they turned out fine but i am no expert either lol

Bobbin thread is much finer than top thread. In FSL you use the same thread because there is no material involved, so you need that heaviness. If I'm not mistaken with the amount of stitches and the density of designs and add the fabric into it you would probably break thread often using top thread in the bobbin.

Bobbin thread is indeed much finer than the regular poly embroidery thread. But I have a Janome 300E, and I used some of Veronika's cat redwork on kitchen towels. I did them in blue, cause the towels were blue, linen-like, not loopy terry. I not only used the same thread in the bobbin as the top because I wanted them to be reversible, but after the first one picking out all the tearaway, I didn't even hoop any stabilizer, just sewed on the towel. I was probably just lucky, but it came out fine, no problems. I do think this Janome, being a simple embroidery machine, nothing fancy, does far more than I should ever ask it to. I never seem to have problems with tension, thread breaks, etc. It's like the Energizer Bunny, it just keeps going & going, no matter what I ask of it. I'd go for it, see what happens. Just don't do it on anything expensive first! Best of luck, Marji

Well, you got some good replies!

I'm with marjialexa. I have a Janome 300E and it takes whatever I throw at it. It never hurts to try different things. Just don't try something on your most favorite t-shirt without testing. Jan

this question and the answers are very interesting for me

I use the bobbin thread when doing projects that don't show on the reverse side. The pre-wound ones have more thread on them than when we wind our own bobbins. Good luck!

There are basically 3 reasons to use bobbin thread: it is less dense than embroidery thread, and it won’t add bulk to your design. Secondly, it costs less than embroidery thread, thirdly, since it is thinner, you can wind much more on the bobbin. That said, FSL uses embroidery thread on top and bottom. Projects that will be viewed from both sides (like the wedding towels in projects that I did recently) use top thread for the bobbin also. There are no bobbin police, so if you want to use polyester as bobbin thread you have permission! The kitty says, "I can do what I want!"

Thank you for all the responses!! And now I know!!!
Flowers & hugs for all of you!!

I agree completely with jrob. Also, when you use embroidery thread top and bobbin you normally use the same color thread in the bobbin. If you do not want the thread to show as much on some projects, you can use the same color in the bobbin - embroidery thread or regular thread - to match the color of the object being embroidered. You do not have to change the bobbin color but match it to the fabric being embroidered.

Thanks for asking the question. Very interesting. I'm one that just follows the directions. Very seldom do I try any other way. :)

very good question thanks for asking