I've been using invisible thread from Superior and just LOVE it! It's a poly thread and comes in clear and in a smoky color. I often use it to machine topstitch my binding on (folded over to the front and topstitched). I always use it in both the top and the bobbin and really haven't experienced any problems with it other than being difficult to actually SEE it when I'm threading the machine and needle. I think the brand/quality of invisible thread you choose does make a difference, and was very reluctant to try it at first. I had some bad experiences with it many years ago (I'm sure it was nylon thread then), but tried it on the advice of a LQS instructor in a binding class. I've used the Superior invisible thread in my Juki, Bernina 630 and in my daughter's Janome 6600, all with great success. I always take the time to check and adjust the top and bottom tension if necessary when I start using it and have had no issues with it.