Prism99

I use YLI nylon filament, and have had none of the problems people warn about. Have occasionally tried other types of invisible thread and don't find them as "invisible" as the YLI.

Mine is on a cone. I use a thread net on the cone and place it in a jar behind the machine. I use an "outrigger" -- just a stick with a hole on each end. One hole goes over the thread spool holder; the thread goes through the other hole.

I use only metal bobbins; plastic bobbins are more likely to distort. When winding, I wind slowly to minimize the stretching of the thread and I fill the bobbin only 3/4ths full to make sure it does not distort the ends of the bobbin.

Are you loosening the upper tension? I don't know how much polyester threads stretch, but the nylon stretches quite a bit, and this requires loosening the upper tension.

Edit: I should add that I no longer FMQ with this thread, simply because I have found I prefer using Aurifil 50wt variegated for most projects. I still use the YLI for invisible machine applique, however; have never found an invisible thread that works better, and I have tried several.