I don't see why you couldn't use 2 strands of floss for applique, it would be easy to match the floss to the fabrics. If you're like me, I have lots of floss left over from my embroidery days, so it would put my "stash of floss" to good use. I would test for whether or not the floss will run - I ruined a fairly complicated cross stitch piece when I washed it and the red floss ran, ruining all that effort.