When I first started trying to learn fmq, I read all the books, Harriet Hargrave and Diane Gaudynski, etc. I can't remember which one or if both said they almost always use monofilament because of the convenience of not having to use different colors of thread and because it makes the stitching look more like handquilting. I started out using it and got used to it but there is a learning curve of sorts. First of all it's like sewing with a hair. I have always used SewArt. There is another brand that is similar and just as good but I can't remember right now the name. The cheaper brands tend to be like fishing line. I usually use cotton in the bobbin but I have used the monofilament in the bobbin and not had a problem with it but you do have to loosen your tension a bit and I can only fill the bobbin half full. It gets really really tight. Also, when filling the bobbin, fill it a little looser if you know what I mean. Wow, sorry for the info overload. Hope this helps. I sure would love to get brave enough to use the beauiful cottons and silk colors on the top and bottom but since I do all my fmq on my domestic machine and my stitches are way less than perfect, I keep using what I'm used to.