The polyester spray filler is used for blocking / staightening. Our product is good to 50 mils! It is a much harder, but not brittle material then ordinary 2K primer, and able to go much thicker. It was designed in Germany for repairing hail damge where the dent is dollied out and sprayed with PE filler instead of skiming with polyester glazing putty. Spraying is much better as you do not get the spreader grooves and it uses MEK instead of cream.