Just now the question of using poly thread with the heat gun came up, so I thought I'd put up some pics
of the tests I did.
first this is the layout, stitched.....4 different meltables- poly and nylon- on top of 4 pieces of cotton.
this is a sheer home dec material, melted really nicely but there isn't enough contrast with the cotton below to see it well.
Moonlight Sonata, 25x42