Invisible thread is sometimes used by quilters to quilt the top of the quilt. Since it is invisible it is not suppose to draw attention. It just gives texture to the quilt. It is used for the top thread, not in the bobbin. It is very fine – .004m.
This thread comes in two colors – clear and smoke. Clear is used on light colored quilts and smoke is used on darker quilts.
Below are two spools of invisible thread. The clear color works well on light colored fabrics and the smoke color works well on dark fabrics. The thread is very fine and should not go in your bobbin. (If you take a class on how to “retool”/adjust the bobbin for special threads then it is possible to use this in your bobbin.)
Both clear and smoke colored invisible thread are pictured below. You can see what the clear thread looks like in the close up photo. It has been used to stitch in the ditch between the blue fabric and the red and white stripe. It is barely visible on the white stripe. The clear thread has also been used on the dark red/rust fabric next to the red and white stripe. The thread is more visible here. If I would have used the smoke color, the thread would be less noticeable.