Thread choice for invisible machine applique
One more question, if I may :)
Why would you choose monofilament over using a matching cotton thread such as DMC or Masterpiece or a matching silk?
For economy and for invisibility...
...at most you'd need just two spools of monofilament—clear and smoke. As I think I mentioned, I'm not a fan of the Superior Thread's smoke color because it looks much to dark to me, more like a regular solid thread.
Since you use a sewing machine to make these stitches, the stitch itself is going to lay on top of the fabric.
That means it's going to show. No way around that!
Hand applique stitches, on the other hand, take a bite out of the fold and then the thread travels on the backside of the background fabric. The only part of the stitch that shows is the 'bite'.
Can you use a more conventional thread?
Absolutely! It's your quilt.
But I think if you do a bit of comparison stitching on a sample as you determine the tension settings you'll need, that you'll like the results from the monofilament better. The stitches will be, well, invisible from a viewing distance. That's the main selling point for me.
If I did choose to use one of the threads you mentioned, I'd choose the finest one, the 100 wt silk, to help camouflage the stitches.
Another potential thread choice
There's a thread out on the market called Invisafil that intrigues me for this technique.
Invisafil is a 2 ply, 100 wt polyester with a matte finish made by a Canadian company. It's a colored, not clear. I've got several spools of it to test this winter. My testing results will be posted on the website when they're ready.
Thank you for your question! I hope you find this information helpful.