What You Get+-
When I applique with felt I usually also add extra embroidery embellishments. Those are the stitches I want everyone to notice - not my applique whipstitches. So I do that applique using the finest thread and thinnest needle I can find.
Invisafil thread is 100 wt. It's like stitching with spiderweb silk! You have to look really closely to see the applique stitches in the photo above. That's exactly what I want.
The other tool needed for nearly invisible stitches is a very thin needle. Stitching in felt leaves a visible hole, so you want a needle that will leave a hold just big enough for the thread to fill it. I use a #11 straw needle - very, very thin. You can get the ones I use here.
One spool of Invisafil holds a whopping 100 yards of thread.
In the swatch photos below, I've also indicated what felt color each thread matches.